The worst customer service

I am extremely unhappy with the service that I have received from my service provider MTN. For the past few months MTN has contacted me stating that I have an unpaid instalment due. In the month of February my debit order failed to go off due to an error from my bank, which I had paid and have P.O.P for. I have then been making my payments as per normal each month and still the problem persists and my phones keep getting cut. I have been to one of their branches multiple times and have also called their call centre and nobody can tell me where the missing payment is coming from. They keep telling me they think it's this month and when I take out P.O.P they then go a month back and tell me that they think it's the previous month as so forth going back another month each time I produce my proof. A lady had contacted me from their accounts department and she cannot explain to me what is happening either and promised to get back to me the same day yet I have not heard from her in a couple of days. Today once again my connection had been cut off and still no answers. This kind of service is unacceptable!