MTN the big *********** *********

Beginning of this year I decided to settle my cellphone contract 100%, and switch over to prepaid. I phoned the retentions department and, after many hours of being on hold and recurring phone-calls because their agents drops calls, got the final settlement amount from them that I need to pay. I specifically asked on the call, are you sure that if I pay this, I owe nothing more. The answer was yes. So I went into a MTN store and paid in full with cash. A while later I start receiving smses stating that I owe money and will be blacklisted if not paid. So naturally I tried phoning. No one at the help center knows why this happened, but can't help me either. So I went to the shop where I paid the money. They are aware of what I paid and can even see that I paid in full on the system, however they can also see that there was some inexplicable billings after I settled 100%. So they try to phone and figure this out as well as get the recording. They then get back to me and let me know that their retentions department refuses to help them. I need to do this myself. How is it possible that an MTN employee can't be assisted to resolve problems. How is it possible that no one at the help centre is able to resolve queries as they do not understand their own system. Then, how can I be blacklisted for a mistake I did not make and then make it as difficult as possible , in fact impossible, for me to resolve this? This doesn't make sense. This is ******** and they should be sued for this type of behaviour. I can refuse to pay the money, but they will then blacklist me and that will affect my credit score. Again, this should be ********. I am continuing this case, however it is costing me to take leave from work to go to MTN shops and wait for hours on phone calls with people who unfortunately are never able to assist in any way other than sell more products to you... How pathetic. Are you competent enough to respond to this?