Bad Customer Relations

I wanna complain about the level of service I am getting from the Matrix call center, in particular the billing/account and cancellation department, I am however happy with the tracking department and the unit itself is impressive, however whenever I try to call the accounts department, they take forever to pick up calls, on top of that whenever they promise to call you back or promise to resolve an issue, they never live up to their promise, I have two vehicles using their trackers, now I have been trying for months to cancel one vehicle and leave the other but every time I call them, them give me different stories and It's frustrating, I have since sold the one vehicle I want to cancel but the debit order is still for two cars because the one car hasn't been cancelled, I was even willing to transfer the tracker onto the new car I bought but even that effort turned fruitless because the one agent told me it cannot be done, whilst the other one told me it can be done at a fee, I have no issue in paying cancellation fees or changing fees, but they keep dodging the bullet