Bad service and *****ing my money

I took a contract at mtn early this year. Around February and the agreement was to pay R200.. Mtn has been debiting more than the agreed amount and some month they months they would make 3 debits in one month.. Im tired because they sometimes cut my line saying that I owe them I can't even get through to their call centre.. Their network is horrible and they busy taking my money. They don't care about their customers they care about making unnecessary debits.