Read and Write Excel using open xml in c#

ReadWriteExcel.cs

    private DataTable ReadExcelSheet(string fname, bool firstRowIsHeader)
    {
        List<string> Headers = new List<string>();
        DataTable dt = new DataTable();
        using (SpreadsheetDocument doc = SpreadsheetDocument.Open(fname, false))
        {
            //Read the first Sheets 
            Sheet sheet = doc.WorkbookPart.Workbook.Sheets.GetFirstChild<Sheet>();
            Worksheet worksheet = (doc.WorkbookPart.GetPartById(sheet.Id.Value) as WorksheetPart).Worksheet;
            IEnumerable<Row> rows = worksheet.GetFirstChild<SheetData>().Descendants<Row>();
            int counter = 0;
            foreach (Row row in rows)
            {
                counter = counter + 1;
                //Read the first row as header
                if (counter == 1)
                {
                    var j = 1;
                    foreach (Cell cell in row.Descendants<Cell>())
                    {
                        var colunmName = firstRowIsHeader ? GetCellValue(doc, cell) : "Field" + j++;
                        Console.WriteLine(colunmName);
                        Headers.Add(colunmName);
                        dt.Columns.Add(colunmName);
                    }
                }
                else
                {
                    dt.Rows.Add();
                    int i = 0;
                    foreach (Cell cell in row.Descendants<Cell>())
                    {
                        dt.Rows[dt.Rows.Count - 1][i] = GetCellValue(doc, cell);
                        i++;
                    }
                }
            }

        }
        return dt;
    }

    private string GetCellValue(SpreadsheetDocument doc, Cell cell)
    {
        string value = cell.CellValue.InnerText;
        if (cell.DataType != null && cell.DataType.Value == CellValues.SharedString)
        {
            return doc.WorkbookPart.SharedStringTablePart.SharedStringTable.ChildElements.GetItem(int.Parse(value)).InnerText;
        }
        return value;
    }

    private void CreateExcelFile(DataTable table, string destination)
    {
        hfFileName.Value = destination;
        lblFileName.Text = string.Empty;
        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<WorksheetPart>();
            var sheetData = new DocumentFormat.OpenXml.Spreadsheet.SheetData();
            sheetPart.Worksheet = new DocumentFormat.OpenXml.Spreadsheet.Worksheet(sheetData);

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

            uint sheetId = 1;
            if (sheets.Elements<DocumentFormat.OpenXml.Spreadsheet.Sheet>().Count() > 0)
            {
                sheetId =
                    sheets.Elements<DocumentFormat.OpenXml.Spreadsheet.Sheet>().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<String> columns = new List<string>();
            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);
            }

            //}
        }
        btnDownloadExcel.Visible = true;
        lblFileName.Text = "Servicing file created successfully";
    }