CAP Security misusing bank details for unauthorised debit orders

Quite concerned by CAP Security's misuse of my banking details. I shared them when I thought I would use the service then changed my mind before the contract was scheduled to start. I informed them of this and they acknowledged. Nonetheless... two months later, I noticed a debit order from them. Trying to get my money back has been an uphill battle. Just shocked that even with written evidence that they are in the wrong, they still have not acted.