Mtn *****ing me every month with taking me on a date

So for the last 8 months MTN have been incorrectly billing me, they have double debited my account on some months, other months not at all and then I need to go into the store because they cut my service, the store manager at cape gate shopping center told me it is because they switched debiting system, so they ran my account in both and that's why I had to pay both, so after months of fighting they took double the money and there is nothing I can do about it, they logged a complaint and told me to wait for a call, it's been 2 months, no calls and no refund. So I've written that off and last month my debit order went off, only to surprise me again at the end of Feb and not debit my account again, and now they have cut my service again, I have spoken to everyone and no one wants to assist or is able to assist, this is disgraceful, all I want is to cancel my serve and leave but they can't help with that either.... Can someone please help and tell me what options I have????