FNB Avoidance

Here we go again. FNB simply does not respond to any mails if you do not complain on Hello Peter... Sent email one week ago, still have not received any feedback other than that they received my mail...

Long Story short:

I made a payment on 16 July 2019 for the exact balance it was reflecting on my online banking to settle the loan.

I just logged in now and found that the balance is no longer 0, but 149.22.

I noticed in the transaction history that the amount is for interest.

Why is this reflecting on the loan? The original amount I took out a loan for was 9000. I paid since January my monthly installments which were 550. This brought my balance to 9,346.60, which is exactly the amount I then transferred. So looking at that, interest must have already been calculated in the balance so why am I still being charged interest?