Cancelation of cellphone contract

I upgraded my Cell C contract on my cell phone number *** however I phoned Cell C to cancel the contract within the stipulated Period. The new device was delivered to me and I phone Cell C and arranged to return the device to them. The device was returned to Cell C on the 28.01.2021 CellC received same om 02.02.2021.numerous telephonic queries was done by myself after noticing that my bank account has been debited as I realized that the said contract was not canceled by CellC. I am currently paying for a device that is not in my possession. I have recently been debited again for the same contract and I don't get any joy from CellC. I would appreciate it if this matter can be resolved asap