Indirectly double debited by FNB

I have been banking with FNB for a very long time and recently they seem to be making mistake after mistake. I made a payment to a 3rd party and got the service from the 3rd party. That was somewhere around the 18 of December 2023. So they FNB did not clear the money or reserve the funds. So from my side the payment was made because I received the service of what I was paying for. Unfortunately FNB systems did not reserve or clear the funds and that is their system fault. Now in 2024 the 17th of January they bill my account for the transaction of 18 DEC 2023 which according to me went through because I got the service that i paid for. I have to pay again for the same service of R3600 TO FNB. Meaning I payed the 3rd party R3600 and now I have to pay FNB R3600. In a way i'm paying for FNB SYSTEMS failure that could not reserve/clear the funds. Even though they don't admit that I'm being double debited because of the failure FNB SYSTEMS FAILURE. Imagine making a payment on the 02 of Jan 2024 and they later bill your account on the 18 of March 2024. Is it how your systems work. Very disappointed. When I call they say it will never happen. Meaning something faulty did happen but FNB just don't want to admit and correct it. In summary the whole thing was caused by FNB failure not clearing or reserving funds from my account and then i have to pay the same service AGAIN.