Cartrack

In December 2017 I took a contract with Cartrack, a device was installed in my car and I thought all is well as I signed the debit order for monthly payment. Two years down the line I was made aware by the company that the device has never worked and I need to call their technician to come and fix the device at my cost, I refused the advise as I was not prepared to pay for the fault that was not mine. Cartrack insisted that i am the one liable for the cost, I requested to cancel the contract because they were not rendering a service to me. They rejected my request sighting the 3 years contract. I started to return the debit orders as I was not willing to pay for a none service , with a hope that they'll eventually come to party. They continued to threatened me until I re-active the debit order but still they were not willing to fix the device. Until today I am still paying for the device that is not working and Cartrack is calling me daily demanding the payment of those debit orders that were returned. I demand that Cartrack cancels the contract and refund my money as they never rendered a service to me.