Harassment from Mixtelematics

I have witnessed abuse at another level after being with this company for close to five years my car was installed with their tracking device, I sold my car last year May 2019 informed them that I have sold my car they emailed me a letter confirming immediate cancelation, now in 2020 I got a letter saying my account is handed over which I'll see my credit score affected, Mixtelematics you are harassing me