Excess Payment - What is it?

Hello there,

For previous month I had a revenue of $12 and CGTrader add another $12 and said that this is an Excess Payment - (Due to a mistake in accounting process, we paid 100% royalties for some of your sales during December-February. We apologise for the inconvenience caused.)

if it's a a mistake in accounting process, why this month CGTrader takes from my revenue this $12 back?

Thanks in advance,

Syoma Pozdeev