Open XML generates only <NewDataSet /> tag from a full Excel file, but work for other files - asp.net

Question

I have an excel file full of data, and I'm trying to use Open XML SDK to convert this file into xml file.
I followed the documentation and other questions here on stackoverflow. However, the output of the xml file is always <NewDataSet />. Knowing that I tried other excel files and it worked fine.
Here is how my excel file looks like:
And here is my code "I tried two approaches":
The first approach is to use DataSet.GetXML(), it returned the same value as the next code does.
var xmlDS = new ConvertExcelToXml().GetXML(filePath);
string xmlPath = server.MapPath("~/UploadedFiles/XML/");
StreamWriter xmlFile = new StreamWriter(xmlPath + Path.GetFileNameWithoutExtension(fileName) + ".xml");
xmlDS.WriteXml(xmlFile);
//The used method to return the excel file dataset
public DataSet GetXML(string filename)
{
using (DataSet ds = new DataSet())
{
ds.Tables.Add(this.ReadExcelFile(filename));
return ds;
}
}
//This method used to return DataTable for previous method
private DataTable ReadExcelFile(string filename)
{
DataTable dt = new DataTable();
try
{
using (SpreadsheetDocument spreadsheetDocument = SpreadsheetDocument.Open(filename, false))
{
WorkbookPart workbookPart = spreadsheetDocument.WorkbookPart;
IEnumerable<Sheet> sheetcollection = spreadsheetDocument.WorkbookPart.Workbook.GetFirstChild<Sheets>().Elements<Sheet>();
string relationshipId = sheetcollection.First().Id.Value;
WorksheetPart worksheetPart = (WorksheetPart)spreadsheetDocument.WorkbookPart.GetPartById(relationshipId);
SheetData sheetData = worksheetPart.Worksheet.Elements<SheetData>().First();
IEnumerable<Row> rowcollection = sheetData.Descendants<Row>();
if (rowcollection.Count() == 0)
{
return dt;
}
foreach (Cell cell in rowcollection.ElementAt(0))
{
dt.Columns.Add(GetValueOfCell(spreadsheetDocument, cell));
}
foreach (Row row in rowcollection)
{
DataRow temprow = dt.NewRow();
int columnIndex = 0;
foreach (Cell cell in row.Descendants<Cell>())
{
int cellColumnIndex = GetColumnIndex(GetColumnName(cell.CellReference));
if (columnIndex < cellColumnIndex)
{
do
{
temprow[columnIndex] = string.Empty;
columnIndex++;
}
while (columnIndex < cellColumnIndex);
}
temprow[columnIndex] = GetValueOfCell(spreadsheetDocument, cell);
columnIndex++;
}
dt.Rows.Add(temprow);
}
}
dt.Rows.RemoveAt(0);
return dt;
}
catch (IOException ex)
{
throw new IOException(ex.Message);
}
}