Get single value of merged cell after active cell

I have got this excel data and would like to access the value of merged cell. Some code I have worked with -

filename = '....\example.xls';
sheetname = 'Sheet15';
string = 'A15';
excel = actxserver('Excel.Application');
workbook = excel.Workbooks.Open(filename);
sheet = workbook.Worksheets.Item(sheetname);
find_string = sheet.Cells.Find(string,[],[],1)
string_row = find_string.Row;                  %ans here is 2
string_column = find_string.Column;            %ans here is 8    
required_stringrow = find_string.Row + 1;         %ans here is 3
required_value = get(sheet, 'Cells', required_stringrow, string_column);       %ans here is NaN

The value of the merged is present always in first cell(B3). So i can access it only from cell B2 with the above code. I get answer as NaN for cells C2,D2,E2,F2,G2,H2 for the above code. Instead I want answer as the value of merge cell. How do i do this??