CARTRACK FAILING TO FIX THE DEVICE BUT EXPECTING PAYMENT

I am currently being harassed by CARTRACK to pay my premiums for a device that is not working. On numerous occasions when I felt like repeating my story to their inattentive consults, I would answer their calls to eask why they expect me to pay when they are failing to come fix the device. As of yesterday, 16th of January 2021, I received an SMS warning me of imminent blacklist on my name because I have not been paying my premiums since last year September when they told me there is a problem with my tracker. Im worried that they want to temper with credit profile due to their neglect. I don't even know if the device ever worked from day one but I have been paying since. My car disappeared in September last year but they could help and now im subjected to their daily phone calls and threats of blacklisting. What must I do?