Useless Cartrack

So I joined Cartrack which was Ohk at first then after a few months I was not able to trace my vehicle via their app, called them and they tell me their unit is Faulty(one that I do not even know it's location on the vehicle) they need to come repair it and I must pay for that? I stopped paying them immediately because they were not able to locate the vehicle till today now they handing me over???? ***