MTN is *****ing my money

Hellopeter is now my last resort. Mtn just don't care about clients. I get a skyrocket bill from MTN every month. When I go to the store, they just say to me it's my data, I bought 4 G data from my fnb account. This month I still have 3 G data left, and again I received a huge bill from MTN, during the month I checked my balance every second day on *141*1# just to make sure that I don't go over the limit and I didn't. I also have another contract with MTN that I never use, I have been trying to cancel that contract since last year September 2015 when it expired. I phoned MTN twice and went to Brooklyn Mall Mtn store three time already to cancel this contract, but it is still going off my account every month. I'm very angry and disappointed with MTN, it doesn't matter if I call or go into a store, I still get the same lame "I don't want/can't help" attitude.