Unfair blacklisting

I was on month to month contract with Cartrack and then last year I requested via email to cancel their services. It seems they did not cancel the contract and kept on charging me. I just found out I have been blacklisted and my account has been handed over. Over the years I’ve paid my premiums on time and consistently but they never recorded that on my credit record and now they are quick to blacklist me?? I regret the day I took signed up for your services!!