Cannot cancel a cancelled subscription

Put in a request to cancel. They first say they cannot find any paid subscriptions. I have to first proof the debits. They go quiet. Next month the debit goes off again, so i query. They find someone else has used my bank details??? They confirm cancellation, and even send me an email to say no future debits will go off, then a week later, another debit goes through. I query and they say i did not give them enough notice...