MTN...Pathetic!!!

I have renewed my top up account at MTN in October 2014, I requested for a zero limit to be added onto my account so I cannot exceed the limit... this has not been done! 4 months later MTN deducts R3186.85 from my bank account without any invoice or notification and after paying my monthly installment of R360!!! This service is pathetic because I land up calling 808 and keep having to deal with different operators! I want this fixed as it is the second month this is happening. I am only suppose to be paying R360 per month NOT R3186.85! I cannot understand how it could take 7 days to give me feedback on whether I would be reimbursed or not! The least that could have been done was to contact me to work out a possible payment plan instead of deducting such a large sum of money for a cellular account! It is not my fault that I have a app**** for this option and their operators were negligent. If I do not get reimbursed I want this contract cancelled! I am never going to renew / open an account with this service provider ever again!