over debited account

my account has been settled on the 26/11/2021. Monday the 29/11/2021 the debit order went off. I've been reaching out for the last three days via email. I've received a email from them "Kindly note should you wish to make early settlement we recommend that you do so at least 5 working days prior to your contractual payment date to avoid the contractual installment being debited." I've rep**** with numerous emails just to be ignored. I went to the bank today just to find out that I can not reverse the debit order. **** POOR SERVICE