Tracking Unit not working but paying

I spoke to netstar people in December 2020 when I wanted to check where my car was and I was told the unit isn't working. They told me that they need to come and install a new unit. They kept on deducting money from my account while my unit was not working.

Everytime I would call and would be sent from one consultant to another to a point one day I spoke to 5 different consultants. I recently called in January and March 2023 asking them to come and install the new device but they still didn't do it.

Last Month in April and this month I decided to go and cancel the debit order because I was paying for the service not rendered. Now they have called me saying that I am behind with my payments.

I want them to refund me for the 2 years and 5 months that I was paying with a unit that is not working.