Poor service

I have a device with cartrack,and I have changed it two times already because it was not functioning and now I have to replace it again because when I press the panic button it does not register in your system. Honestly I'm tired of paying for a service that I do not get,How many times do I have to change my devices before you actually put it a device that actually works....What if I was at an emergency situation and I pressed the panic button only to find out that it doesn't work....I am tired of calling your offices to report that the devices you put in don't work. I am paying every month without fail and yet I am not receiving my monies worth!!!! My contact details are *** Name: Bongiwe Mbonambi.