Bad service from Dstv Multichoice

I have been charged for premium package while I am on Access package. I have called mulitichoice several times, spending a lot of time on the phone, but they still refuse to accept that I have never opted for premium package. I even have proof that I upgraded my package to Access and not premium but they still continue to refuse and they maintain that I must pay for the premium package. This is a very bad service, it is either they do this to several other people or their system is not to be trusted.