Poor service

I am not happy with the service I am receiving from Telkom. My contract was upgraded when I spoke to the agent I was not informed that I still have to pay extra for my devices. The agreement was that my monthly payment will stay the same. They have admitted in an e-mail that I am paying the incorrect amount. The e-mail was send to the relevant department for feedback but it is almost two weeks with no feedback. It is now two months that I have been billed the incorrect amount. I need feedback as soon as possible from them.