Bad service

I have a mtn contract, which I took 6 years ago, I currently have 3 contracts with mtn. For the first time mtn debits me an amount that we did not agree on. They are suppose to debit me R210, but they went and debited me R439. I then called them and asked the reason, they did not have a reason, I was told it will be fixed, I will be called a week later nothing happened I then called again and I discovered that nothing was done on the first query. They re-logged the query and another week pasted and still no response from mtn. This is the most pathetic service ever. They are very *********** even the team leader, because I even spoke to a team leader, but did nothing with my consents. Want they are doing is a way of *****ing our monies daylight. How do you do that, such a big company like them.