Mtn keeps taking the wrong amount from my account

The last three months MTN took more than a R1100.00 from my bank account without my permission. My cell phone account ***) was at a total of R328.00 per month. The account consist out of a R300 top up airtime, 500 MB data and 50 free sms's. The only way you can get in touch with MTN is by calling the customer care number. So I went to the shop in the Kathu Mall and spoke with the consultant. He send my bank account statements to the billing department. On which they said that MTN will credit my account the next month. This does not happen. My account was again debited with over a R1100.00 on the 17th of March. I haven't received any credit or any money paid back into my account. The consultant at the store tells me that he can only send them my bank account statement so they can give me credit. This leaves me without words. I only want the amount that was taking wrongfully from my account and that the correct amount will be deducted from my account from now on.