Tracker demamnding payments for services not rendered

Since late March my tracker unit has not been updating. I contacted Tracker but it was during lockdown so they only contacted me in June to check it. After checking it, it only worked for a few hours and the next day it was again not working. a technician was sent again to fix the unit in July but again it never worked. In short they haven't rendered services to me since March but surprisingly they demand payment. I stopped making payment and they have referred to their lawyers for collection.

they demend payment siting the fact that they contract is still in effect but forgetting that they have breached the contract.