The worst service!

My contract was coming to an end on the 25th November. I was told that I must phone in on the 24th of November which I did. Spoke to guy and said my contract is canceled. Much to my surprise I phoned in December to confirm that my contract was canceled but it was not canceled according to the lady Wendy I spoke to. I have been **** to And I was still paying for a monthly bill.she said she canceled the contract but that's hard to believe as I have a bill for January. Again I have been **** to . After numerous emails with customer care and retentions department that doesn't bother to respond back. All I want is my contract to be canceled and my number to be on prepaid.