Cartrack refusing to cancel contract - paying for a faulty unit

CARTRACK unit not working after 2 years. Cartrack is refusing to cancel my contract. I had so many tracking units in cars before without any problems and now having problems with Cartrack unit after only 2 years. I had to phone Cartrack to ask if my unit is still working, because I was used to getting frequent sms messages from other tracking companies before, stating that the unit was tested and working. I received a sms from CARTRACK to register on the CARTRACK app and when I did, saw that my vehicle position was not updated for over a year. I then phone the Cartrack call centre. On enquiry, the Cartrack technical department said that my unit is faulty. I then wanted to cancel my contract because of poor customer service and refusing a replacement of the unit, they tested the unit again and then said it was working and gave me the correct location. The app still shows a location of over a year ago, on enquiry Cartrack again said the unit is faulty. I am refusing replacement because they took the whole car apart when fitting the unit. A car is just never the same when taken apart, breaking factory seals. I'm now paying R250 a month for a faulty unit and I do not even know when it became faulty. I had to phone CARTRACK to find out if my unit was working after 2 years of installation.