3D graph in Excel

Preapre first Pivot table using months as columns headers, agents as rows headers and sum of sales amount in data.
Then draw your 3D graph from this Pivot table.

If you provide a sample of data (paste the data into a code block; I won't open a workbook), I can show a few non-3D chart approaches which would be easier to read than any 3D chart you could draw in Excel.