FNB takes my money but Flight booking is unsucessful due to no space on flight

I tried booking a ticket today on the FNB app, just for it to say it was unsucessful but the bank still took my money, when i phoned it was said it was due to the flight not having enough space and that it will be reversed with in a hour, hour passed phoned again and then they said as soon as it is in their account they were reverse it to me. I mean how can the bank make a mistake like that. Now I have to wait for them to reverse this. Now how long will that take, I am really not happy! I would really like to have answers as when this will be sorted out!