Refund

I had an account with Cartrack for over 2 years. In April this year, I called to cancel my account with them. That same month, Cartrack debited more than they were supposed to. They debited R268 more. I called them and the call center agent acknowledged the mistake and said it shows on the system and I should go reverse it at the bank. I went to the bank and was told they cannot reverse it because it already reflects on my bank account. I called Cartrack again and was told that they don't reverse anything below R268. I have been calling ever since trying to get my money back and no one has been able to assist me from Cartrack. The question I have is why did they debit money they were not supposed to? It's their mistake and they're not willing to assist me. I want my money back.