Unauthorised debit order - mony is unsafe

Discovery owed me a refund from previous membership and asked for updated bank details. Knowing what idiots they are, I deleted the clause authorising debit orders and specifically wrote on the form that I am NOT a member and DO NOT authorise debit orders. Lo and behold, Discovery debits me instead of refunding me! In regards my banker, how can TymeBank allow this payment from my account without authorisation?