Sending letters of demands after failing to replace unit following tragic accident.

I had a Beame unit installed in my car in 2018 but sadly, i had a tragic accident the same year and that vehicle was written off. After my insurance had paid out, I notified Mixtelematics of my misfortune and kindly requested them to replace/install a unit in my new car so i could carry over the account in the new vehicle but they refused. After numerous calls and emails to their *********** and rude customer service consultants, I was eventually told that the unit i had was not replaceable so i was basically expected to pay for a unit that was sitting in a s**** yard somewhere. Now they're sending me letters of demand and they're threatening to hand over the account but they have failed to replace or install a new unit in my new car. So now i must pay for something i don't have??? How fair is this??? What kind of customer service is this??? I'm so disappointed because i really liked the fact that their unit was easy to hide and the installation was non-intrusive which meant there wasn't any easily detectable wiring but after the way they've treated me, I'd strongly advise everyone to avoid this company by all means!!! This is the worst car tracking company EVER!!! Their customer service is really disgusting.