CARTRACK, NON -EXISTENT, BUT YOU KEEP ON PAYING

I have signed a contract with the company, CARTRACK in Dec 2014. They have installed a tracking system in my vehicle, as requested by my short term insurer. The vehicle was secured every night at my residence in a lockup garage in the house with an alarm system. Till July 2015 Cartrack have contacted me every time I went away overnight when the vehicle was not at my home address. They have phoned me to ask if I am aware that my vehicle is not at home. This happened about three times until Jul 2015. From July 2015 to July 2017 Cartrack has never contacted me again. Since July 2015 I have been on a number of trips to the west coast, Lamberts Bay and to Herm**** on the east coast over night. But they have never contacted me to tell me that my vehicle was at places I normally do not visit. Cartrack has created the impression by me that everything is in order, they always know where my vehicle is. In Nov 2016 I decided that I want to sell the vehicle. When I contacted them at first I did not say that I want to sell the vehicle I first wanted to find out the steps how to cancel the contract. It was then that I realized that they do not have a clue where my vehicle is and that they did not have any idea of my vehicles movements since July 2015. When I confronted them about the issue a guy at the call centre said that he think there is something wrong with the tracking system on my vehicle. I said but if you know there is a fault on the tracking system why did you not contact me. He said that they did contact me but could not get hold of me. I rep**** by saying that I have no evidence, emails, sms or phone calls as proof that they contacted me and why would I lie about this, it is my property at stake. So this is the problem : I have been paying for a system or a service that is non existent for 2 years. When I ask them to cancel the service they said I must complete a cancellation form. When you try to complete a cancellation form on the website you have to ok at the bottom of the form that you agree with everything on the form making you liable for everything they want you to say. If you do not agree with everything on the form you can't send the form and the cancellation has not been filed. They do not acknowledge emails as a form of cancellation and consequently if the contract is not cancelled with the wording that suits them the unpaid amount on the account keeps rolling on. The unpaid amount is just 7 months payments since I do not own the vehicle anymore. I have contacted them now 6 times by email and phone. The only response is their threads with legal action and blacklisting. How is this that a company can get away with bad service to the public like this? Forcing and threatening you to pay for no service?