Changing information without my permission and rude operators

I recently upgraded to a new contract. Since then I have only been having problems. My usage limit keeps on changing. Some days I can use my phone, some days not. When I upgraded I made the limit R200. Since then it has been changed to R2000 and then unlimited and now tonight I heard it is R0. So I cannot do anything because some unknown person decided to change it to R0. Can someone please explain to me how this happens. I have been sitting with a red face, because I cannot do cellphone banking because of my limit that is now R0 without my permission. When I called, the operator was extremely rude and couldn't change it for me. She told me to do it myself. When I tried that, I got a message "Please contact your service" provider...... So if my service provider cannot help me, and I cannot do it myself, what else is there to do????? This is the WORST service ever. Please can you fix your mistake!