At my wits end with Netstar!

I'm at my wits end with this company! My car was fitted with their tracker through the insurance I took out with Dotsure. Years have passed since I owned the car and still Netstar debit my account. No amount of calls or emails seems to get them to cancel my contract. I even have their debt collector hounding me with harassing messages. My statement is 0 yet there seems to be no one who does the actual paperwork. Or is that someone in the company is trying to *****ulently debit my account? Once again, I will go to my bank this afternoon to reverse the ******** amount Netstar took off my account at 20:00 last night!