IMPOSSIBLE TO SORT THIS PROBLEM OUT!!!!!

During last year some bright spark at MTN Accounts decided that my FIXED 2 year 50 top-up contract at a cost of R189.00 per month for the 24 months,.should be an open contract and because of this I received a bill for over R300.00. I have repeatedly contacted MTN, either direct at Rivonia, by phone and walk-in at Northgate branch and today received a message that my account is overdue by R109.42 (which goes up in leaps and bounds every month) and that the lines will be suspended in 2 day's time. Regardless of reference numbers and being PROMISED THAT I WILL BE CALLED BACK, nothing has happened to-date. I am really tired of running around, so far being pleasant, and wasting my time when obviously nothing is going to be done. They want their money and that seems to be their position. I am not paying money I do not owe!! It would be nice to get someone of a managerial position to contact me to sort out this problem - here's hoping!!! Now a visit to Rivonia has to again be made.