IMPROPER CONDUCT

My Policyholder debited my Account twice. I have visited ABSA Bank to reverse one of the payments wherein I have been informed that Debi checks cannot be reversed and I need to speak to the Policyholder. ABSA Bank nor the Policyholder have consent from me for double deductiona yet ABSA Bank is refusing to refund the addional payment. What I don't understand is this Debi heck that the Banks automatically change. If no Consent was provided for double deductions how is it possible for my Bak to allow this?