Cancellation

I have been trying to get my contract cancelled and to get the unit removed from my car. I am now convinced that no one works at the retentions/cancellation department as I have made numerous phone calls and they never answer, on my last attempt I gave up after holding for 20 minutes. E-mails are just as useless because they don't reply. I need someone to attend to this matter urgently. Can someone please cancel my contract immediately. I contacted the people that fit the unit and they claim they can only remove the unit upon authorisation from tracker which is proving to be impossible at this stage.