MTN messing up my name

I was called by MTN sales offering me a phone and I was not interested but I told them I want a contract with airtime and Data which was approved and I was told that I have cancel before a certain period of time if I'm not happy. When it was deliver I received two (2) Sim cards and I wasn't happy I called immediately(same day) and told them I don't want them and they must be cancelled then I was told to take the Sim cards to the MTN branch and I did within that cooling off period, I wasn't provided with anything to say it's cancelled because they can't return Simcards but phones but still left the Simcards. I've called MTN and spoke to more than 10 people and I was told it will be cancelled, when I call and ask records on the system. I'm told my account was sent for cancelation. Today and every day I'm getting calls from VVM collection company saying I'm owing MTN and I'm listed. Not that I can't afford to pay this account but this is not fair.