MTN taking more than they should

I upgraded in November last year to a contract that was 690 per month. i am now being debited odd amounts ranging between 825 and 855. I find this unacceptable and breach of contract. This also can not be out of bundle data or voice as we can not call or use internet once the monthly bundle runs out and must buy prepaid and load said data or airtime onto the phone. No one is helping me and I have had enough. I will being pulling these debit orders back.