Account suspended

Approximately 2 weeks ago, I got an sms that I have an outstanding balance of R133 and my account will be suspended. Not knowing where this amount comes from, as I am on a top up account and I pay a fixed amount every month, I tried calling MTN customer service centre. I kept getting cut off after holding for 10 minutes(happens whenever I call MTN). I then went into Tokai MTN store and they admitted that I was billed extra for the previous month, but they could not confirm where the amount was coming from, so they removed the amount from my account and reactivated so I could make calls again. Yesterday the same thing happened. I got an sms that my account will be suspended if R133 is not paid immediately. This morning my account was suspended again and again I tried calling the call centre and keep getting cut off. This is outrageous cutomer service. I am ever so sorry I renewed my contract with MTN after having so much trouble with them in the past as well.