Cell c refuse to cancel my contract.

I have never had so much trouble to cancel a contract as to what I am facing with cell c at the moment. I have been trying to cancel my contract with them since August 2018, I made contact with them to cancel the contract but it has fallen on deaf ears after many attempts. For the past 5 months I have been trying to cancel my contract but instead they try to sell me an upgrade which I am not interested in. I still get billed every month for something I don’t even use anymore it’s feels like my money is getting ****** from me. This is ridiculous and unacceptable.