Range.MergeCells in Matlab

I am trying to perform a cell merge on an Excel file from Matlab. I don't know anything about this, but tried to use some code I found elsewhere online and adapted it a bit:

Excel = actxserver('Excel.Application');
Workbooks = Excel.Workbooks;
Excel.Visible = 0;
Workbook = Excel.Workbooks.Open('C:\Users\path&filename*.xlsx');
for k=1:length(B)-1
    rng = [ExcelCol((k-1)*MaxH+2),num2str(1),':',ExcelCol(k*MaxH+2),num2str(1)];
    procrng = [rng{:}];
    Range = Excel.Range(procrng);
    Range.Select;
    Range.MergeCells = True;
    Range.HorizontalAlignment = xlCenter;
end

ExcelCol is a user-defined function I found online that converts column number to Excel alphabet notation. It works - no doubt about it.

But when I run & step through the code, I get an error at Range.MergeCells = True. I get: "Undefined function or variable True'.

Can you please help?