Poor Service for Cancellation

I am a Tracker Client, I have sold the car the unit was in, I have been trying for a month to get them to cancel the unit and that I can pay to stop the service. All attempts to contact them has failed. They send an SMS to say we have tried to contact me via my phone, this is a strange response because I don't even have a missed call.

I tried via phone and email and the response is that its a duplicate request so they delete them both. I responded to the email and that also goes unanswered.

I am saddened that this is the service they offer to a customer who wants to pay them money.