Cartrack refuse to cancel unauthorized contract

I have never signed up with them on any contract as I am with another supplier. Since 2019, I cannot get them to cancel the contract without wanting to penalise me. I have called. I have emails. I am at witts ends as to what to do. My Bank refuses to stop the debit order unless I can prove cancellation. What is a person to do if Cartrack keeps ignoring your request?