Settlement amount did not settle the account

I had a personal loan with FNB. I requested a settlement amount and paid the amount. 5 days after I made the payment fees and interest was added to my account. Leaving my account still open. When I queried they said it was because of me settling my loan early. Today I noticed that on FNB web page, they advertise no penalty fee if you settle your account early. I would like to request another settlement amount, who can I talk to that will give me proper, accurate and trusted information so that this does not happen to me again.