Disgusting SERVICE from MTN's Supersonic

I subscribed to Vumatel a while back and got excellent service from them. Recently they were bought over by Supersonic who are part of MTN. Gosh since then I have got horrific service. I have been trying to change my password for about 3 months now and have really been given the run around. Simple excuse from them they cannot change password cause it's not their router. I must login and change but when I do I cannot change it PLEASE HELP