Bad Service Nedbank HomeLoans

We have a home loan with Nedbank and unfortunately trying to get proper feedback and direction from their Home Loan Section has been a hassle since we started with this loan. We have a home loan amount which is impacted by the interest rate. The interest rate has recently changed twice however our home loan repayment amount seems to be continously changing over the last few months even when there are no changes in the interest rate or the amount. We raised this concern and was provided with a generic response that Nedbank reviews this repayment but with no details on what basis. It was excalated and we got a generic response. We said please show us how this was calculated and still no response. I can understand when the repayment changed when the interest rate changed and loan amount changed but if these factors did not change why had the home loan repayment being changed. Can someone please help!!! We are desperate for some comprehensive feedback and not generic responses that have nothing to do with our specific home loan.