How is this my mistake. The mistake is taking out the policy.

Carrack was installed on my son's car, I paid the debit order it was easier. In Dec the vehicle was sold. So I wanted to cancel, I was advised by the accounts department that it would cost me R2000 plus to do this. So it was decided to move it to my car. It was moved. My bank account was debited with R675 and then R218 for Jan and then Feb R195 and R218 I called and they advised that I had shortpaid on the transfer and that they tracked my account and took the money off. That it was my fault that I hadn't made arrangements. They debit my account so how is it my fault? I would like the system removed when the contract is complete. Because the after sales service is shocking. The lady I was speaking to dropped the call. And told me it was my mistake.