CARTRACK disappointing service

It was the most unpleasant experience,

I bought a demo vehicle nearly brand new, I was forced to make use of a tracking company when I financed my car.

When they installed the tracker they damaged my car seat since Feb 2019 was it not repaired.

The tracker installed drained my car’s battery in various occasions to appoint where I had to replace my battery, when I contact Cartrack they denied that it was their device but after the phone call did the problem stopped, my assumption is they don’t take responsibility of poor fitment or problems with their devices,

Due to Covid 19 and loss of income did I contact them to cancel the contract because I could not afford the service anymore they could assist or compromise at all, we had to pay a cancellation fee of R1700 we made arrangement to pay it off over 6 months that they proposed,

We agreed and pay the the first installment end of July, there after we are getting threatening phone calls to take the account legal with these calls the agree we cancelled and that we made arrangements to pay over 6 months but claim the system automatically calls and send smsses.

The threat with summons that will be delivered at my work, when I call them to asked about the sms, they claim I can just ignore the sms.

Although Cartrack confirmed that unfortunately the calls and smsses will continue until we settled the full amount that will be end of Dec 2020,

Surely I am not the only client that have to go through these threads after I made arrangements, and surely the system need an upgrade to not list or bombard clients that made arrangements and pay,

Is it legal to be threatened in this manner by any company?