90% Interest on my loan because of FNB'S MISTAKE + Pathetic customer service

I am absolutely sick and tired of this bank and the problems they give me.

About a week ago, I app**** for a R1000 personal loan on their banking app. It was approved and the loan was paid out. However, when I received the payout, I had received R7000 (instead of R1000). I immediately called FNB to make them aware of this mistake. The lady I spoke to told me that it's "not a problem. Just transfer R6000 back into the loan account and we will get our accounts department to restructure it for a R1000 amount."

This past Tuesday (7 working days after the payout), I had still not received any such feedback that my loan was restructured. I phoned FNB back and was told that it had been restructured on their end, despite me not receiving any feedback. The lady said that she would e-mail me an account statement on which I'd be able to see that the restructuring was done.

She sent me a statement... on which it stated absolutely nothing about a restructuring. On my FNB banking app, it still shows that I owe nearly R900 interest on a R1000 loan... (i.e 90% INTEREST RATE??!!).

I went into the bank today, sat there in the queue for 30min+ only for my ticket to be called and me to be told "Oh sorry, we can't do anything about your problem as its regarding an existing loan. You will need to go back home and phone our helpline" Now I'm not even going to complain about how ridiculous it is that I cannot go to the bank and resolve an issue with the bank, that was caused by the bank... I'm sure common knowledge would be able to understand why that is ridiculously pathetic...

Anyways, went back home. Called the bank. The lady tells me that the reason why I am getting charge almost 90% interest rate (R1900 repayment on a R1000 loan) is because the initiation fee for the loan was based off of the R7000 that was initially paid out and that she was unable to help me.

FNB now expect me to pay a R900 "INITIATION FEE" for THEIR OWN MISTAKE.

Absolutely ridiculous. At this point I am so fed up that I am going to most likely be switching to another bank when all this is done. Absolutely pathetic FNB.