FNB not refunding double debit

I'm frustrated because on the 30th of April I had a double debit of R459 on my account. Initially my banking App all my debit order transactions showed twice and I thought it will be sorted which was exempt for this one. I've been calling FNB Call Centre to reverse without any luck. Yesterday I went to the branch and I was showed the process on my App on the COVID-19 option. I elaborated on the double debit. Yet till now, there has been no update regarding the reversal. I have wasted money and airtime trying to sort it out between my bank (FNB) And the service provider that double debited but no luck. I'm frustrated that FNB is not helping at all.