Cant cancel tracking unit contract

I have cancelled my insurance with dotsure about a year or 2 ago. When I was insured with them they made me install a netstar tracking unit on my car. Now the 3 year contract with netstar is complete and I would like to cancel that contract. Netstar said I should ask dotsure to remove the device from the insurance policy before they can be able to cancel the contract. Dotsure is busy sending me from pillar to post and not doing what has to be done for me, this is really frustrating because I dont understand why they actually dont remove it from the policy as soon as you cancel the insurance policy. This is an unnecessary inconvenience to me!