Netstar are *******!

Do not fit a tracker in your car with Netstar! My experience has been terrible to say the least. I took out car insurance with Dotsure and they said that Netstar would fit a tracker as part of their service. A year and a half later, I sold the car and cancelled my account with Dotsure. However, Netstar continues to debit my account. No amount of emails or telephone calls gets me closure. Netstar can't prove that I have a contract with them and yet they refuse to cancel their service for my car. I cannot understand why they expect me to pay for a service that benefits the stranger who bought my car. I am not in a financial situation to afford paying for something that gives me no benefit. They change their debit order dates and take money off my account at random times. To me this is theft. They've just debited again R926.17 from my account which leaves me with less than is needed for my legitimate debits coming off tomorrow! What can I do to stop this? I'm at my wits end!