Fnb temp loan technical error now my problem

I took up a temp loan of R2000 on the 5/02/21 after using some of the funds on the 6/02/21 I had an available balance of about R800 on the 7/02/21 the available balance increased to about R1200. No additional money was paid into my account. When I viewed the temp loan outstanding balance it increased to R2700 something from R2207. When I queried this on the 10/02/21. I was told that I did not repay the previous temp loan in full and this was due to a technical error. My question is why was my available balance increased with R500 if this amount was owing on the account, why was I never notified of this and why does fnb not take responsibility for this error. They rather treating me like I did something wrong with a don't care attitude. Why must I be inconvenienced with something that I was not aware of and I am being held accountable for fnb's technical error