Still being billed

I have 4 cell numbers on my account. In September two numbers were upgraded. I was told that one of my contracts were paid up and needed to call Retentions to cancel it (as we were no longer using that number. I phoned in October and was told that since that the number was in use for the month I could only cancel at the end of the month. I phoned on 25th October and cancelled and was given a reference number and told that the contract was cancelled. I phoned again early November - after receiving my statement and seeing that i was still being billed for this number - and was told that the contract was cancelled and that I would not be debited for it. I see today that I was debited for this contract.