R500+ overcharge on contract

I signed for a R1199 p/m contract with MTN over a year ago. I am now being debited R1758.86. I have sent an email to customer care and have had no response. It is impossible to get through to anyone at the call center. This serves as a notice to MTN that if my account is not credited as a matter of urgency I will have no other choice but to reverse the debit order and block MTN from debiting my account going forward.