Getting error while using OpenXML for Excel Export

Question

i'am trying to export data to Excel. For that purpose i use OpenXML.

The Structure of the Excel should look like this:

 

My current Code: 

public void CreateExcelDoc(string fileName)
   {
       using (SpreadsheetDocument document = SpreadsheetDocument.Create(fileName, SpreadsheetDocumentType.Workbook))
       {
           WorkbookPart workbookPart = document.AddWorkbookPart();
           workbookPart.Workbook = new Workbook();

           WorksheetPart worksheetPart = workbookPart.AddNewPart();
           worksheetPart.Worksheet = new Worksheet();

           Sheets sheets = workbookPart.Workbook.AppendChild(new Sheets());

           Sheet sheet = new Sheet() { Id = workbookPart.GetIdOfPart(worksheetPart), SheetId = 1, Name = "Test Sheet" };

           sheets.Append(sheet);

           workbookPart.Workbook.Save();


           SheetData sheetData = worksheetPart.Worksheet.AppendChild(new SheetData());



           // Constructing header
           Row row = new Row();

           row.Append(
               ConstructCell("Vendor Name", CellValues.String),
               ConstructCell("Vendor Mail", CellValues.String),
               ConstructCell("Vendor Adress", CellValues.String),
               ConstructCell("Vendor Phone", CellValues.String));

           // Insert the header row to the Sheet Data
           sheetData.AppendChild(row);

           ServicesExportDataProvider dp = new ServicesExportDataProvider();
           var vendors = dp.GetVendors();



           // Inserting each vendor
           foreach (var vendor in vendors)
           {
               row = new Row();

               row.Append(
                   ConstructCell(vendor.VendorName, CellValues.String),
                   ConstructCell(vendor.VendorMail, CellValues.String),
                   ConstructCell(vendor.VendorAdress, CellValues.String),
                   ConstructCell(vendor.VendorPhone, CellValues.String));

               sheetData.AppendChild(row);
           }

           InsertEmptyRow();



           Column column = new Column();
           Cell cell = ConstructCell("Info", CellValues.String);
           column.Append(cell); //  **<--- Creates the Exception**


           sheetData.AppendChild(column);




           worksheetPart.Worksheet.Save();
       }
   }

I can export the "Vendors" - Lines. But if i try then to Create columns to Export the "Item Information" vertically, i get the following error:

 

Non-composite elements do not have child elements

Column column = new Column();
 Cell cell = ConstructCell("Info", CellValues.String);
 column.Append(cell); //  **<--- This line throws the error

I can't figure out the problem. Do you have any ideas? How can I Export data in the structure of "Item Information"?