Cancelled service but car track still wants to deduct and are now threatening me with legal action.

I have two months ago sold my vehicle and called car track to inform them that I no longer have that vehicle and they should cancel my policy. The good thing is that the person on the line even said to me that it was now actually on a month to month contract as the 36 month contract was complete and that Its just a matter of cancellation on their side, which she confirmed to me that she cancelled. To date I am still getting calls from cartrack whenever the new owner removes a battery or for their alerts and I keep telling those who call me that I no longer own the car and that I cancelled the thing. They are still even trying to debit. They are even sending me threataning sms's and emails and are now threataning with credit bureaus and such for who knows what?? Is someone not doing their job that side?? I was actually now planning to install them also on my new vehicle but with this kind of shenanigans, I don't think they will get my business again.