Hopefully after speaking to the broker everything will be resolved.
Is he the selling agent and list agent? Dual agency? It's possible the bank has reduce the commission and now he wants you to pay that reduction? "pay more for his fee"??? Did you sign something stating you would pay him something? I may not have all the details but something doesn't smell right. Contact his managing broker and ask for clarification. Interesting. Can you let us all know what happens?