Mtn worse service

I have been a happy vodacom customer all my life until the past 4 years when i switched over onto mtn. Biggest mistake! The customer service is terrible no one is ever willing to assist you. I am on a contract where i suppose to be paying R450 a month there is a limit on my contract but for the past few months mtn has been deducting R569 from my account. Why are you debiting extra?