Cancelling Contracts and Accounts Made Literally Impossible by Mr. Price

I paid off my Mr. Price Home card about four years ago and since then I have been into store 3 times to cancel and have phoned about 5 times to cancel, because they keep billing me for a mobile contract I did not sign up for and did not collect. Each time I have tried to cancel, I have once again paid off the outstanding amount so that I can cancel. Each time I have been told that it is closed. One consultant tried to convince me to collect the simcard and use the airtime but I declined this, because I already have a contract, I don't need it and communicated as much. Yet, I keep getting billed for this simcard that I never app**** for and don't use!!! Despite having paid hundreds (possibly into the thousands) for again, something I DIDN'T APPLY FOR, don't need and do not use, I have been threatened to be turned over to the collections committee because for the past 3 months I haven't paid....BECAUSE I CANCELLED or at least thought I had after the assurances it had been cancelled. I find it disgusting that they make it not just difficult - but impossible to cancel something you didn't apply for and do not use - essentially just taking money. The CHEEK of it to still send me warnings after trying to cancel all this time and affecting my credit record which is otherwise very good. Can someone Senior from Mr. Price please step in - because I feel like I'm trapped and getting ****** and being defamed on my credit record. I'm really desperate and I can not call your call centre again!! Or go into store again. I'm losing my sanity and I do not want to receive another bill, let alone threat from Mr. Price ever again!