THEFT!!!!

I had originally opened my cellphone contract with Nashua Mobile. Nashua Mobile had closed and MTN had taken over, the contract was R199 a month, since MTN has taken over they are overcharging me, the amount is never constant, one month it will be R388, then R397 then R400.22. I have contacted MTN customer care as well as our local branch in town. MTN has charged me double for recurring data, I was then told by customer care on two separate months that MTN would credit my account as this is a fault from their side. I then monitored my account the following month to see and no credit! I have not only called to report but had emailed MTN customer care several times! This is THEFT!!! how can MTN charge me double and not answer me as to why this is happening... Its now 7/8 months later and they still charging me double! I have now refused to pay my account! I am now being suspended for not paying R400.22 but the R199 as my original contract states! THIS IS THEFT! MTN HAS OVERCHARGED ME WELL OVER A R1000, MTN BETTER CREDIT MY ACCOUNT OTHERWISE I WILL TAKE LEGAL ACTION!!!! I suggest nobody takes a contract out with MTN because they are pathetic and useless!!!