Unauthorized debit order.

Who are this people, and did they get to know about my account as I don't remember ever having a policy or providing my details to such a company or association. This people just collect money from my account as and when they want and the debits cannot be reversed as they are locked. I tried on several occasions to trace them or their contact number to no avail. I need all the money they have debited from my account and really, I wouldn't stop at anything until I find out who they are and how did they get into my life to an extent that they have enjoyed ripping me off so much without any show of remorse.