Fixing Excel read/write issues (System.IO.FileNotFoundException) in .NET Core using IExcelDataReader and XLWorkbook

public void AddExcelData(string FilePath)
{

	System.Text.Encoding.RegisterProvider(System.Text.CodePagesEncodingProvider.Instance);

	try
	{

		FileStream stream = File.Open(FilePath, FileMode.Open, FileAccess.ReadWrite);

		//ExcelDataReader Nuget needed
		IExcelDataReader excelReader = null;
		try
		{
			if (FilePath.EndsWith(".xls"))
			{
				excelReader = ExcelReaderFactory.CreateBinaryReader(stream);
			}
			if (FilePath.EndsWith(".xlsx"))
			{
				excelReader = ExcelReaderFactory.CreateOpenXmlReader(stream);
			}

		}
		catch (Exception)
		{
			throw;
		}

		var result = excelReader.AsDataSet(new ExcelDataSetConfiguration()
		{
			ConfigureDataTable = (data) => new ExcelDataTableConfiguration()
			{
				UseHeaderRow = true
			}

		});
		DataTableCollection table = result.Tables;
		
		//gets first sheet
		DataTable curTable = table[0];
		stream.Close();

		curTable.Columns.Add("NewColumn");

		DataRow rw = null;

		//appends new row to the last used row
		rw = curTable.NewRow();
		rw["NewColumn"] = "Row data";
		curTable.Rows.Add(rw);

		//XLWorkbook Nuget needed
		XLWorkbook wb = new XLWorkbook();
		wb.Worksheets.Add(curTable, "Sheet Name");
		
		//overwrites the file
		wb.SaveAs(FilePath);

	}
	catch (Exception e)
	{
		Console.WriteLine("Unable to generate excel : " + e.Message);
	}

}