Appalling non-service from Altech Netstar

I have had 4.5 month ongoing negative experience with Netstar after being a customer since 2011. I have an account for 3 cars. In January we replaced one vehicle, and I sent an email to Netstar to cancel the vehicle tracker, providing the consultant's name and location of WEBUYCARS where the vehicle was so that the tracker could be removed. TO BE NOTED: the installer of the tracker of the replacement vehicle said explicitly that the tracker on the new vehicle would automatically replace that on the old vehicle and would not remain on our account. A second vehicle was replaced in April, after which I sent an email informing Netstar of the sale and asking for cancellation of the tracker-bearing in mind that the installer had said the new tracker would replace that on the sold vehicle. To date, I have sent a barrage of emails over the almost 5 months, attempting a response from Netstar, and made several phone calls to the customer centre, without any action being taken. I have both sold vehicles plus 3 vehicles on my account, and am still paying for 5 instead of 3. A consultant phoned me 3 weeks back after a negative review that I sent in response to an email from Netstar requesting a review to the 'resolved issue', and after explaining all to her, and re-sending all my emails as proof, have still had no recourse. Let it be noted, that at NO time did Netstar respond and let me know what the procedure should be to replace one vehicle tracker with another. I received no communication nor response whatsoever on this particular issue, besides automated responses with reference numbers. The Customer Care service is manned by incompetence and no accountability to or regard for the customer. Another huge irritation is that the two sold vehicles' whereabouts appear on my Netstar app-something that brought my attention to the fact that these vehicles are still on my account and being financed by me, whilst being driven by their new owners. I am at a loss as to how to proceed, as I have 3 vehicles with trackers installed. This service is simply appalling!