10 months later and still contract is not updated!

I signed a new contract 10 months ago, after emailing customer services repeatedly, contacting MTN via twitter, posting a complaint on Hello Peter and visiting the branch where I took out the contract - I am still overcharged by approximately R200 per month. After 10 months MTN finally told me it was due the fact that they had a systems failure an the contract didn't update and that they are not able to rectify this now but they have been able to move my payment date from the 7th of each month to the 25th without my permission. As MTN is clearly in breach of a contract I have repeatedly said that I want to cancel my contract but they keep deducting their monthly fee plus the extra R200. With this level of incompetence I will never be able to cancel this contract