File.WriteAllText()

I have used the below code to write data into Excelsheet.
 File.WriteAllText(@"C:\CourtInitiationFiles\ExportExcel.xlsx", "Court initiation");         -- For Main heading purpose
File.AppendAllText(@"C:\CourtInitiationFiles\ExportExcel.xlsx", sb.ToString());            -- Actual data (It contains column header and values.)
After this  my excel looks like below..
Court Initiation                                                                                    -- Wrong place
S.No                            Name &nb ...