Mtn overcharge and do not resolve matters

My 3g data contract has gone from an average spend of R105.00 per month to R2800.00 in July. I reported it to the branch at the mall. A month later I phone the call centre and i was informed that the person did not follow the right channel. I went back and the person were not available. It was then logged by a lady. A month later the branch said i must phone the call centre. I phone from the branch. They explained to the guy how to do it. Again two weeks later i decided to phone the call centre and again the lady said that no feedback has been given and logged it again. It is now again two weeks later and still no response. This seems to be the norm. As I know two other people with the same problem. They take your funds but do not give back if they are in the wrong. Please check my latest reference no if you are from Mtn. ***