Refund from Telkom

on the 23 August 2024, I overpaid Telkom the sim of R617.00 by mistake using my Standard Bank app, of which is the account I have been using for the past 12 months, I called them, their promise to pay back my money, and they also asked the bank account to use, I gave them my bank details, but deposited the money in my old account which is FNB,and unfortunately I am no longer using that account. I went to FNB to ask if they can do something about the error Telkom made in this closed FNB account, they said they cannot assist due to the FNB account not active. Till today Telkom is not following up on this matter and they are not taking this seriously. I need my refund back as soon as possible.