Installation :
1.https://www.microsoft.com/en-us/download/details.aspx?id=30425
or
2. https://www.nuget.org/packages/DocumentFormat.OpenXml/

Adding Reference :

• DocumentFormat.OpenXml
  
• WindowsBase
  

 Ref : https://msdn.microsoft.com/en-us/library/office/bb456488.aspx


Write Excel

public void ExportDataTable(DataTable table, string destination)
        {
            using (var workbook = SpreadsheetDocument.Create(destination, DocumentFormat.OpenXml.SpreadsheetDocumentType.Workbook))
            {
                var workbookPart = workbook.AddWorkbookPart();

                workbook.WorkbookPart.Workbook = new DocumentFormat.OpenXml.Spreadsheet.Workbook();

                workbook.WorkbookPart.Workbook.Sheets = new DocumentFormat.OpenXml.Spreadsheet.Sheets();

                //foreach (System.Data.DataTable table in ds.Tables)
               // {

                    var sheetPart = workbook.WorkbookPart.AddNewPart();
                    var sheetData = new DocumentFormat.OpenXml.Spreadsheet.SheetData();
                    sheetPart.Worksheet = new DocumentFormat.OpenXml.Spreadsheet.Worksheet(sheetData);

                    DocumentFormat.OpenXml.Spreadsheet.Sheets sheets = workbook.WorkbookPart.Workbook.GetFirstChild();
                    string relationshipId = workbook.WorkbookPart.GetIdOfPart(sheetPart);

                    uint sheetId = 1;
                    if (sheets.Elements().Count() > 0)
                    {
                        sheetId =
                            sheets.Elements().Select(s => s.SheetId.Value).Max() + 1;
                    }

                    DocumentFormat.OpenXml.Spreadsheet.Sheet sheet = new DocumentFormat.OpenXml.Spreadsheet.Sheet() { Id = relationshipId, SheetId = sheetId, Name = table.TableName };
                    sheets.Append(sheet);

                    DocumentFormat.OpenXml.Spreadsheet.Row headerRow = new DocumentFormat.OpenXml.Spreadsheet.Row();

                    List columns = new List();
                    foreach (System.Data.DataColumn column in table.Columns)
                    {
                        columns.Add(column.ColumnName);

                        DocumentFormat.OpenXml.Spreadsheet.Cell cell = new DocumentFormat.OpenXml.Spreadsheet.Cell();
                        cell.DataType = DocumentFormat.OpenXml.Spreadsheet.CellValues.String;
                        cell.CellValue = new DocumentFormat.OpenXml.Spreadsheet.CellValue(column.ColumnName);
                        headerRow.AppendChild(cell);
                    }


                    sheetData.AppendChild(headerRow);

                    foreach (System.Data.DataRow dsrow in table.Rows)
                    {
                        DocumentFormat.OpenXml.Spreadsheet.Row newRow = new DocumentFormat.OpenXml.Spreadsheet.Row();
                        foreach (String col in columns)
                        {
                            DocumentFormat.OpenXml.Spreadsheet.Cell cell = new DocumentFormat.OpenXml.Spreadsheet.Cell();
                            cell.DataType = DocumentFormat.OpenXml.Spreadsheet.CellValues.String;
                            cell.CellValue = new DocumentFormat.OpenXml.Spreadsheet.CellValue(dsrow[col].ToString()); //
                            newRow.AppendChild(cell);
                        }

                        sheetData.AppendChild(newRow);
                    }

                //}
            }
        }
   

Read Excel File

     public static DataSet ExtractExcelSheetValuesToDataTable(string xlsxFilePath, string sheetName)
        {
            DataTable dt = new DataTable();
            DataSet ds = new DataSet();
            using (SpreadsheetDocument myWorkbook = SpreadsheetDocument.Open(xlsxFilePath, true))
            {
                //Access the main Workbook part, which contains data
                WorkbookPart workbookPart = myWorkbook.WorkbookPart;
                WorksheetPart worksheetPart = null;
                if (!string.IsNullOrEmpty(sheetName))
                {
                    Sheet ss = workbookPart.Workbook.Descendants().Where(s => s.Name == sheetName).FirstOrDefault();
                    if(ss == null)
                    {
                        throw new Exception("Sheet name not mathced");
                    }
                    worksheetPart = (WorksheetPart)workbookPart.GetPartById(ss.Id);
                }
                else
                {
                    worksheetPart = workbookPart.WorksheetParts.FirstOrDefault();
                }
                SharedStringTablePart stringTablePart = workbookPart.SharedStringTablePart;
                if (worksheetPart != null)
                {
                    Row lastRow = worksheetPart.Worksheet.Descendants().LastOrDefault();
                    Row firstRow = worksheetPart.Worksheet.Descendants().FirstOrDefault();
                    if (firstRow != null)
                    {
                        foreach (Cell c in firstRow.ChildElements)
                        {
                            string value = GetValue(c, stringTablePart);
                            dt.Columns.Add(value);
                        }
                    }
                    if (lastRow != null)
                    {
                        for (int i = 2; i <= lastRow.RowIndex; i++)
                        {
                            DataRow dr = dt.NewRow();
                            bool empty = true;
                            Row row = worksheetPart.Worksheet.Descendants().Where(r => i == r.RowIndex).FirstOrDefault();
                            int j = 0;
                            if (row != null)
                            {
                                foreach (Cell c in row.Descendants())
                                {
                                    int? colIndex = GetColumnIndex(((DocumentFormat.OpenXml.Spreadsheet.CellType)(c)).CellReference);
                                    if (colIndex > j)
                                    {
                                        dr[j] = "";
                                        j++;
                                    }

                                    if(j == 21)
                                    {
                                        // only for checking
                                    }
                                    //Get cell value
                                    string value = "";
                                   // if (c.ElementAt(0).Count() >0)
                                      //  value=  c.CellValue.Text;
                                     value = GetValue(c, stringTablePart);
                                    //if (!string.IsNullOrEmpty(value))
                                    //    empty = false;
                                    dr[j] = value;
                                    j++;
                                    if (j == dt.Columns.Count)
                                        break;
                                }

                                //foreach (Cell c in row.ChildElements)
                                //{
                                //    //Get cell value
                                //    string value = GetValue(c, stringTablePart);
                                //    //if (!string.IsNullOrEmpty(value))
                                //    //    empty = false;
                                //    dr[j] = value;
                                //    j++;
                                //    if (j == dt.Columns.Count)
                                //        break;
                                //}
                                //if (empty)
                                //    break;
                                dt.Rows.Add(dr);
                            }
                        }
                    }
                }
            }
            ds.Tables.Add(dt);
            return ds;
        }
     
        public static string GetValue(Cell cell, SharedStringTablePart stringTablePart)
        {
            if (cell.ChildElements.Count == 0) return null;
            //get cell value
            string value = cell.ElementAt(0).InnerText;//CellValue.InnerText;
            //Look up real value from shared string table
            if ((cell.DataType != null) && (cell.DataType == CellValues.SharedString))
                value = stringTablePart.SharedStringTable.ChildElements[Int32.Parse(value)].InnerText;
            return value;
            
        }

        private static int? GetColumnIndex(string cellReference)
        {
            if (string.IsNullOrEmpty(cellReference))
            {
                return null;
            }

            //remove digits
            string columnReference = Regex.Replace(cellReference.ToUpper(), @"[\d]", string.Empty);

            int columnNumber = -1;
            int mulitplier = 1;

            //working from the end of the letters take the ASCII code less 64 (so A = 1, B =2...etc)
            //then multiply that number by our multiplier (which starts at 1)
            //multiply our multiplier by 26 as there are 26 letters
            foreach (char c in columnReference.ToCharArray().Reverse())
            {
                columnNumber += mulitplier * ((int)c - 64);

                mulitplier = mulitplier * 26;
            }

            //the result is zero based so return columnnumber + 1 for a 1 based answer
            //this will match Excel's COLUMN function
            return columnNumber;
        }