Disappointing services from MFC division of Nedbank

I have been a MFC client just for over two years, however the service that i have been getting from them for the past three months, it is extremely disappointing, MFC has been deducting the wrong amount for my car installment for the past three months and every time i have to call so that they can refund me, which is exhausting and inconveniencing me as a client, i am really disappointed.