Have they ****** my money?

I cancelled a Debit order online 10 working days before the new month. This debit order still went off, however the money that was debited never reflected into my account, so i called their helpline to inquire about this a week later(thought maybe it needs time to reflect into my account). When I finally got thought to a helpful consultant, they informed me that their system only sees the last debit order that was taken in April and nothing for May ( money was taken in May). I emailed the prof of debit order and all other relevant information to the email that was provided by the consultant. Two weeks later and nothing, no money reflecting in my account or returned to my account it was debited from. At which point can i consider this theft of my money?