Credit dept not capable of crediting my account

On the 10 th of september made payment into mtn account and as yet after 5 calls to the custmer service dept and 3 visits to their stores with proof of payment my account has not been credited. Mtn are not willing to let me speak to anyone in their credit dept ,everything needs to be logged with customer service, not one person has called me back after telling they would. Now I get an sms saying if account not paid my line will be suspended.