Changing NumberFormat to DATE of an Excel Cell (Range) out of matlab with ActiveX

I am struggeling to change the cell attribute (to date) out of matlab via ActiveX.

WorkBook.Sheets.Add([], hExcel.ActiveSheet); % add a new sheet

row1 = {'Heading: ', [] , []}; % define top row with heading
row2 = {'Start Date: ', [], exceltime(Output_Struct.MetaData{1,4}.DateStart)};
row3 = {'End Dat: ', [], exceltime(Output_Struct.MetaData{1,4}.DateEnd)};   

TableWithMetrics  = [row1; row2; row3];
eActivesheetRange = get(hExcel.Activesheet,'Range',['A1:C', num2str(3)]); % 
eActivesheetRange.Value = TableWithMetrics; % write the cell array into selected area in the active sheet
   
% formatting
top1row = hExcel.Activesheet.Range('A1');
set(top1row.Font, 'Size', 20); % apply formatting to the selected range
set(top1row.Font, 'Bold', true);

datecells = hExcel.Activesheet.Range('C2:C3');  
 % example out of the excel macro recorder : Selection.NumberFormat = "[$-407]d. mmmm yyyy;@"
set(datecells.NumberFormat, '[$-407]d. mmmm yyyy;@');

---> Result:

Error using set

Invalid handle

Error in createXlsReport (line 205)

set(datecells.NumberFormat, '"[$-407]d. mmmm yyyy;@"')

OK, then i try not to use set...

datecells.NumberFormat('[$-407]d. mmmm yyyy;@');

---> Result:

Index exceeds matrix dimensions.

Error in createXlsReport (line 207)

datecells.Numberformat('[$-407]d. mmmm yyyy;@');