I did not upgrade!!!! I ASKED TO CANCEL MY CONTRACT!!!!!

I contacted the call centre on the 11th of December to cancel my contract after the 24 month period has ran out. The lady went on and on about the loyal customer I am and they will give me discount, at the end I said to her again, I want to cancel the contact, not upgrade and she hang up. I phoned again and the second lady was very helpful. She confirmed that the contract will be cancelled. Beginning of January another premium was deducted from my account, which I then reversed because according to my knowledge this was cancelled. I phoned Vodacom to enquire and was told that I upgraded my contract in December and the premium they will be deducting is x5 more that what I use to pay. I explained the story and they said a manager will contact me but I need to keep in mind that there will be cancellation costs... this after I clearly instructed them to cancel. Still waiting for someone to contact me... and dear not pay your premium then they will blacklist you.