Shocking customer service and playing games as they refuse to cancel my subscription

Really shocking service from Cartrack, Ive been with Cartrack for year and didn't get much service from them. At some point my husband suspected that my device wasn't working, I eventually contacted them and they confirmed that my device hasn't been working for months if not years but no one bothered to notify me. I then asked them to cancel, instead of cancelling Im now getting calls from different agents and letters of demand as apparently my account is overdue. The funny part is they refuse to cancel this subscription even when I told them to cancel numerous time and was very clear that I'm not happy with their services.