Bad customer service Cartrack

I have 2 cars installed with Car Track device and the devices are not working for last few months and made many complaints but not resolved.I have been following up with them via call centre and sent multiple mails but of no use.I am paying for nothing for many months and let me know how to lodge a legal complaint towards them and they must refund and I want to cancel the contract without any penalty as I am cancelling due to the service delivery failure.Can any legal attorney's help here