Contract amount WRONG

I've got a MTNChoice200 contract @ R669 for 24 months with MTN. I am in my 3rd month now. I keep within my data and minutes and even have minutes left. But MTN deducted R1114.77 and then R799.00. After phoning 808 and speaking to Thato I was informed that she has escalated the enquiry and that someone will phone me back in 7 days time. (808 by the way is a number one doesn't get through on easy) 14 days have passed now and still no one phoned me back ,so I phoned again. Now they want to log a query again. I told the lady that it will be the second time and that no one phones back. I need to speak to a manager. The manager however is in a meeting and is not allowed to phone back. I am supposed to go into the branch again to sort this out. I asked what my contract with MTN states? They can not tell me anything about their OWN PRODUCT! But they deduct money every month. So I must show MTN their own contract. The call centre is a absolute joke if they don't even know the terms of my contract.... how the hell can they assist me then? MTN is deducting more money than the should on my account and they must refund me PLUS interest.