I want my paid up letter as I do not owe you anything

My contract with vodacom came to an end on the 1st of January, I have been calling them to cancel my contract but they always say I did not pass what what process. I don't want to pass anything, what I only want is my contract to be cancelled with them and receive my paid up letter and that is that.i have been paying these people every month without fail, even when they increased my bill every month I still paid cos I knew I binded my self with the contract, now the contract came to an end but they do not want to cancel it. Please vodacom, I need my paid up letter as I do not owe you anything