Incorrect billing for services not in use

Good day. I am an existing DSTV customer for 15+ years. I now opted for the R799 Explora deal. I was not informed that I will be billed from the day I receive the decoder. I accepted the service on 30 Dec 2014 and received the decoder on 7 Jan 2015. I contacted DSTV to confirm when I need to cancel my existing service and activate the new one. It was explained that I can do that on the 1st of Feb 2015 as I already paid for Jan. Now I have a bill of R2338.54 for services that I did not use. I am now liable for their mistake. The call center agents were sort of helpful and friendly, but one was very rude and did not want to assist. She wants to cancel my current subscription (which I payed for by debit order) in order to resolve the problem. I have been sent from the one person and number to the next and Multichoice can apparently not assist with my account. Please help!