Is banks suppose to take more or are they just *****ing

2 weeks back I app**** for a temp loan of R450 which I figured would cover an outstanding debit , when I checked to confirm it was the amount requested it seemed correct but when I logged back in I found that the account was R4500 , I immediately tried to reverse the total calling into FNB which was closed I even tried the supposed bankers which wasn't much help I called the ***** line. In short I reached out to everyone to assist but to no aval. The next day I finally got hold of someone who told me that they will reverse the total but I will still have to pay the initiation fee of R500 + - , Now my problem is I tried my best once I saw the error to return it , at this point I didn't use any of the funds and another point is the payback is more than what I requested. At this point I will be giving FNB free money. I feel its a complete rip of cause how can I be charged for something I tried my best to return and your system doesn't have fixes in place is that the service that FNB is selling? I'm really keen on leaving this banking institution due to this matter