MTN unable to do a sim upgrade

I have been a subscriber to MTN for more than 25 years. I have tried to upgrade my contract (SIM upgrade) for more than 6 months now, without success. Many calls, many emails from my side but I get promised that all is now in place and will have the new contract loaded with in 4 hours, just to find that it has not been done. I have pleaded with MTN to advise me, what the issue/problem is so that I could rather move on and get a new service provider, however this question could up to date not be answered.