tracker not working

I phoned tracker to have my unit tested because I didn't get a sms as usual to say that my tracker is in a good order.<br> <br> The lady who helped me said that I will receive an sms within 72 hours. After a week I phoned them because I didn't received any sms from the company.<br> <br> Now they advise me that the unit is not working and I must pay an amount so that the technician can come fix the problem. I pay every month my fee as agreed on, why do i need to pay for the repairs as i am still paying a monthly fee for a unit that doesn't work. Surely tracker should incur the repair costs. What would have happened if my vehicle was ******? I want to cancel my contract because I don't get any service.