FNB being FNB again. Not helping anyone

So here we go again with FNB. So I took out a homeloan from them about 7 years ago. Did not miss one single payment. As a matter of fact, I paid way more than I should have on my bond repayments. So now I sold my house. On FNB's banking platform it showed that my balance is X amount. FNB then took an additional 25k for who knows what on top of that. I logged a query with them on the online banking platform and it was resolved without any feedback whatsoever. So I guess the best way to contact them is to complain about how bad they are. The only positive thing that came out of this is that my new home is no longer financed with FNB. Neither will I finance any business decisions with them in future. Pathetic service. If they bothered to answer my query, it wouldn't have turned out this way.