Cancellation of contract

After I sold my vehicle in August last year, I emailed Cartrak to inform them to cancel the contract, they just ignored my email, after that I emailed a couple of departments to inform them the vehicle was sold, no one came back to me. Now, after I phoned them to cancel to contract, they said I have to pay R730 outstanding fees as well as another month cancellation fee. A bit unfair don't you think?