Defective device - defective service

I had a tracker installed as part of my insurance policy with Oakhurst Insurance from Netstar I was eager to have it done at a discounted rate as I drive alone 99% of the time. I have cut my ties with Oakhurst for bad service as i explained to them that when I had my accident the tracker didn't do what is was supposed to & I had to contact for help. Now Netstar feels I am liable for the contract cancellation, I feel it is appalling they want to make me pay for a device that wasn't working as punted by them & Oakhurst. I asked & they agreed to get the recordings but negated in getting the ones where I complained asked them to update details which they hadn't either eg most importantly my registration number - how you going to look for a ****** car if you have the incorrect registration number.