Cancelled account in June but still get billed

I have sold my Toyota Fortuner in May 2015, I have cancelled my Tracker in June and accepted to still pay for June. Tracker has billed me in July again and I cancelled the transaction at the bank. Now they have billed me again on a other description number. Now I must take off at work to go and reverse the transuction. Please help I am struggling to cancel tracker account. I am paying for a service that will not be met because I don't own the vehicle any more. I have spoken four times with Tracker over the phone and emailed the responsible perton twice.