Cannot reach anyone who can assist

I want to purchase an internet bundle and tried doing it using the USSD codes. I was always able to do this. Suddenly it says I am not registered for self service and to contact the call centre, but the call centre keeps me on hold for 5 minutes and then the call just drops! Over and over again. In the mean time they are charging me insane internet rates!! I cannot reach anyone who can help me and I am paying too much for my internet. MTN scores by not making anyone available who can help me.