Cancelation of tracking device

I owned a car last year and I took insurance with A&G they requested netstar to fit in a tracking device in my car, I sold the car in December and canceled the insurance. Now netstar is debiting money from my acc monthly when I call them to enquire they tell me am indebted to them for next 36 months even if I don't own the car. Told them I can't pay for something I don't use they went through to say they are handing me over.

They refuse to cancel the tracker too.