contract still not cancelled

<p><span style="color: #555555; background-color: #ffffff;">was delivered a faulty device by cell c online on 1st week of Feb, after notifying them that I got the tablet faulty when I got it they took in and informed me that they would have the matter sorted out and I'd get a new device, weeks later I went to pick up the phone and it still had the same problem.I then requested to have the contract canceled end of Feb already it's 2months later and the debit order is still going off, no cancellation quote was given and I found out they never took back the phone from the store as I never took it back after I saw it had no speakers. I've called the contact center numerous times and the last person I spoke to hung up the phone.why am I still being billed for a faulty device that I returned back to them in time?my rights state that if I take out a contract on line and it is not what I requested I have the right to cancel it. I'm not even using the sim card because I ***umed it would be cancelled same month I requested.</span></p>