Data theft!!!

Good day, I have been struggling with MTN for sometime now. I have cancelled my contract and still not getting anywhere. I had a basic data package with mtn. I used this sim card in a ****le which I use to access my emails etc when I am away from desk at clients. My usage is always really low, my debit order never changes. In July this year, a much higher debit order went off my account and again in October. Your staff at the local MTN shop have checked and there is definitely something strange going on. My July bill, we can literally see a straight data transfer being done off my sim card. It wasn't me, I didn't authorise this. I have been back and forth since. My mtn cell number is ********** . This was cancelled in October, but you should be able to see the history. I am not happy at all with mtn. I am tired of this waiting game. Right now, seems like someone at MTN has ****** from me. Please look into this and sort it out before I take it further.