Theft and incorrect benefit from ME

I took a personal loan with FNB and I tried to settle it by paying a lump sum into the account last year, Now I am still paying the same amount and same interest and same credit shortfall based on the entire loan. When I call to enquire why I am still paying the same amount, interest rate and credit shortfall based on the initial amount, I am informed That I should have arranged restructuring when I paying. HOW MAY I SUPPOSED TO KNOW. The bank is now benefitting from an incorrect figure as if it is the initial amount. I am leaving this bank faster than I anticipated.