I have to pay extra dividend tax due to an FNB share mistake?

FNB shares did not implement my dividend tax reduction application for my American portfolio. This was app**** for in Feb2021. I was informed that my application was accepted and the account was opened. Only recently did I discover that I was paying 30% tax on the dividends instead of the 15%. Now when I enquired about it, was I told I have to re-apply as my old application was out of date. Now I have to pay for a mistake they made? That is not fair.