Vehicle tracker cancelation drama

I took out a tracker last year with this company. I sold the car in July this year and I asked that they cancel the tracker since I sold the car. They told me I have to pay over R600 to settle it. I told them that's too much and why should I settle. Imagine, my installment for it is about R90pm. I was told I have a 3 year verbal contract with them. They told me they would make the recording available. I have been waiting for the recording since August. I sent an email to remind them but they have not bothered respond or send the recording. I am irritated with this company because they are still debiting my account but there is no proof of a 3 year contract. How unprofessional...