Debited account, when invoice had been paid a month previously!

Fidelity-ADT debited my account for repair of the alarm system on 17th November 2017, causing my account to go into arrears, with concomitant costs levied by the bank. I had paid this bill promptly after the repair on 21st October 2017. Further, proof of this payment had been emailed to the Accounts Department on even date. I called the call centre twice this morning. On the first occasion, the agent promised to send me an email, to which I could reply attaching proof of payment. No email was forthcoming. I called again, and duly sent the proof of payment to the agent Katlego Tshabalala, requesting that she confirm receipt of my mail, and that the matter had been escalated to Credit Control. 3 hours later, I am still waiting