Complain to Netstar about my car track service

I had a contract with netstar from 2019 in fact since I bought a car. Last year if I am not mistaken my car tracker had some problems I couldn't see it via the app and I sent them an email we made an arrangement. So they sad the technician will come on Saturday everything was confirmed. The technician was supposed to come around 1o o'clock. And on Saturday morning one of their consultants phoned me and said their technician is no longer available they will re schedule my appointment with them. Till today They hadn't contacted me. So lat year late around October if I am not mistaken I sent them an email canceling the contract with because they failed to render services for my car they told me about the cancelation fees so I decided to join another tracking company because Netstar did not care about my wish.. And yet they have put my name on bad debts.. Pls help how can I resolve this problem