Paying for a service I said I did not want

Answered a ph call from a Vodacom call centre offering cell phone insurance. I said I was not interested as I've never taken out insurance on my cell phone and ended the call. That was about 2 months ago. I now have cell ph insurance on a Sim card I do not use. Calls are recorded...how can Vodacom get away with this? I went into a store to have the insurance cancelled...only to be told they could not. Surely this is *****ulent?