MTN OVER CHARGING FOR NO REASON

I have always used MTN always had contracts. My normal bill is about R600.00. Last month during the month all off a sudden my line got suspended. All my payments are up to date I even got a statement showing its up to date. I called MTN they said my account is in arrays for about R1600.00 I said that's impossible lady couldn't give me a valid reason why my account is in arrays she opened my line only because I agreed they can debit my account at the end of the month which they did I even went to the MTN store they don't even understand why I got charged so much. As a loyal customer of MTN who is now coming to the end of his contact you are giving me good reason to port to another network