TRACKER'S UNIT NOT WORKING

I am very much concerned about tracker. I have received numerous calls from them advising me that they cannot see my car, the device installed in my car is faulty. So I said they can send out a technician to check the device, I was told I have to pay a call-out fee for the technician to come. Meantime tracker is debiting my account every month for this service. Whose responsibility is it to ensure that the service is rendered. They have told me that the guarantee of the unit has lapsed. How do I know that tracker is not trying to make money from me. I think this is absurd. They need to make sure that I get the service I pay for every month. Why is tracker doing this? If I do not have the money to pay for the technician what will happen? I have asked the call centre agent to request their supervisor / manager to call, but up until this day no one has called. I am sure tomorrow I will get another call from the call centre agent to tell me the same story! I AM SO ANGRY WITH TRACKER!