Still paying for a service I cancelled repeatedly

In May I went to the Vodacom shop in Key West, Krugersdorp. I requested several services: A contract upgrade, transfer of a data line and cancellation of the other data line. I signed a pile of papers and was assured that all jobs had been done. Since then I have been charged monthly for the data contract that I cancelled. The first month I assumed I was paying a months notice. When I continued to be charged, I called the customer service centre and was told that my data line had not in fact been cancelled. They informed me that it was a problem at the shop and could only be dealt with there. When I again had opportunity, I went into the shop in Key West and queried it. The consultant that had originally helped me no longer worked there. I was told that they could cancel the data contract with immediate effect (and no charge at month end) but that a refund was impossible as it was only my word that I had requested a cancellation. Despite being unhappy I proceeded with the cancellation. Imagine my annoyance to find that I have yet again been charged for the data contract at the end of this last month. Vodacom is taking my money and needs to return all of it forthwith.