Netstar continue to debit my account WAY AFTER the policies are cancelled!

I had 2 cars with a Netstar Tracking device. I have been trying to cancel 1 policy for a car I sold for 3 years and the other 1 for 7 months. I was billed and paid for the 1st car way for 2 additional years as I was told I never accepted the 'cancellation email'?????????????? This is after NUMEROUS emails and telephone calls. I was billed and paid for the 2st car way 5months as they never responded to my NUMEROUS emails and telephone calls to cancel. I finally received cancellation letters for both cars (with an effective date of November 2020 - which is a joke in itself). Today I have received a new statement billing me for November and December. Question is how do I get Netstar to stop billing my account???????????????????