Very poor service

I'm very upset and I regret doing business with Cartrack. I phoned Cartrack to test my unit and check where my vehicle was, they could not locate it until they realised my unit was no longer working, so I complained I had been paying for nothing. I changed my unit for a new one in Jan 2021 and they promised to cancel the previous two debit orders for old unit. Up until now they still nag me with calls for the outstanding balance they promised to cancel. I'm not happy!