Extremely poor service

Extremely poor service, it is now more than six months that my tracker unit is not working but billing has not stopped and my account is being debited as an when they wish which resulted in me stopping to fund my bank account due to bank charges which at the end affected other providers and coursing me a bad name with my bank. Since I stopped paying car track I get their phone calls every day to be told that I am owing. I have on numerous occasions pointed out that I am not getting any service from them and they don't care about it but they are only interested on the money coming in. I have on numerous occasions attempted to reach out to the management but to no avail.