Unacceptable customer experience with MTN customer service

I have been an MTN customer for over 20 years and I recently took out a new contract with them at Mall@reds. The contract was for 36 months and a trade-in deal for the Samsung S series. The value of the trade was R14,400 to be amortised over the 36 month contract period. Unfortunately the phone was recently ******. I called Customer care to find out what the early termination fee would be. An amount +/-R26,000 was shared per the system. I disputed the amount and explained to the Customer care agent the balance of the trade-in that should be taken into account but I was referred back to the store as the trade-in value was not reflecting on the system and the agent indicated that the store should add the credit to my account. I went back to the store at Mall@reds and the lady who assisted me spoke to her colleague at retentions and explained that they cannot add the credit to my account as they did not have access to edit customer accounts. The lady who assisted me at the store emailed all the necessary documents to retentions but nothing has happened. I have been following up for over a month now and everytime I call I have to explain the whole story just to be told they cannot assist me or refer me to another department. I called back again today and spoke to a supervisor in retentions who told me it's a billing issue. I then called again and explained the story to billing and asked to speak to a supervisor in billing but instead the agent transferred my call back to retention. I was told the supervisor would call me back in a few minutes and I'm still waiting.vThis is ridiculous because I have spent so much time and no one in MTN between retentions and billing can assist me. The store escalated the matter to the regional manager but I have to date not received a response. This is unacceptable for a customer to have to struggle and spend so much time with a service provider and a team who does not know how to handle their own products. The excuse is that it is the 1st time that they deal with an early contract termination that involves a trade in. Should someone not investigate this find a solution and get back to the customer? Is it really that complicated? Luckily I have terminated my contract I had for the last 20 years with them and will be moving to another service provider. I just need to resolve the trade-in contract with them.