The worst tracking company!

I had Netstar as my vehicle tracking company for about a year. They would debit my account monthly and I never had any issues. I then traded in the vehicle and advised them on 11 November 2024 that I would like them to cancel the tracker as I am no longer in possession of the vehicle. They then sent an email back saying my request is referred to retentions and Andile Nkosi from customer services asked “cancellations” to assist. I made a follow up on 04 December 2024 as Netstar debited my account again and I asked what the progress of the cancellation is and I got no response. In January 2025 I get several calls from Netstar on a daily basis telling me I have an unpaid account and I owe them something like R400-something Rand. I indicated to the lady that I had requested two months ago that this contract be cancelled as I no longer have the vehicle. She told me on their system it’s not cancelled so I am liable to pay them. How can I be liable to pay people who did not do their job on their side? If I indicated to you to cancel it and you acknowledged my email how are you still billing me? Is this not daylight ******* to continue billing someone after they have cancelled. They now have a collections office calling me for money that I cannot possibly owe them if they had just done their jobs and cancelled my contract when I requested it. How can I be liable for this account? I have written proof of the times I emailed and followed up. This is the worst tracking company I have ever had!