MTN incapable in solving simple problem

It seems impossible to make any contract changes once locked in by MTN. My problem is simple yet seemingly impossible to solve. I renewed my contract May 2021 and since then the data portion has become insufficient as I changed jobs. All I need to do is either add more data by migrating to a suitable option or to add a data package to my contract. None of which I am able to do. I tried to buy data via my bank account but get an error, I tried to buy AfriHost mobile data but they cannot add my number to their network either. I went to two separate MTN shop and got referred to a number that cannot help me either. SO NOW WHAT! I want to cancel my contract, return the handset and try with another service provider (perhaps Vodacom know what they are doing) but I do not know how to do that either. Solving my problem should not be this complicated.