Shocking Accounts Query handling

I've been with MTN (contract) for >20 years. I've had a problem with their billing / accounts department for going on 10 months! A new credit card issued in Jan required a change of number details. Not processed - therefore payment rejected. I received demand from CSS solutions in June. I paid outstanding amount to them. I have since paid each month by EFT. I have no arrears and am actually one month in advance. I've phoned the MTN call centre, sent emails and got reference numbers MTN Refs *** + + + ,and automated letters - each saying query will be addressed in 8 hours. Please note - 8 HOURS. I get calls and emails from CSS Solutions at least 3 times a week to say "further action will be taken". Precious was very helpful and understanding and gave me the name of her supervisor - Moyake - to address mails to. Did that a month go. nothing has changed and calls and mails continue. I cannot get the name of, or transferred to a manager at MTN and all mails are automated and do not provide a person to address mails to - they apparently just go in to a great big anonymous void. I have just received the 9th INCORRECT invoice and statement from MTN which still do not reflect my EFT payments!!! I've mailed PoPs to both CSS and MTN. No response! No resolution! my fear is that they will disconnect my number which would have devastating effects for me! Why can't someone in MTN and/or CSS take ownership and record paymentsand issue the correct Statement, remove me from any possible poor credit rating list, and sort this 10 month old problem out. What is so difficult?!