Unable to upgrade for almost 5 months

I've been trying to upgrade since the beginning of April. The phone I wanted (CAT B15Q) was advertised in the Yellow Trader but I was told it was out of stock for weeks. When the strike started A MONTH AND A HALF LATER I had still not received it. In the meantime the newer model (S50) became available and I ordered it instead. They didn't have that in stock either. And they still don't. How can MTN advertise a product and not have it in stock for so long? Attempts at having this resolved have amounted to nothing, and neither my nearest MTN store (Jeffreys Bay) nor MTN Direct has been able to assist after numerous phone calls and visits over the last 4 months. The only response I get is that there is nothing they can do. I logged complaints and were promised to be contacted by a customer care supervisor within 24 hours - I was never contacted. MTN is clearly not concerned about the exceptionally poor service I am receiving. I have been a loyal customer for 15 years. MTN would not be as patient as they expect me to be if I decided to not pay my account for nearly five months. I honestly don't know what to do anymore to get to do something as basic as upgrading my contract.