Is that really legal? How does a firm sign off on an amount and then a MONTH later find out that it shouldn't have happened and take the money back?
To me that would be like winning a slot jackpot in Vegas and then them coming back after I was walking out of the casino and telling me that the jackpot wasn't supposed to be that high and I had to give the money back.
Personally I'd already be with that money on a small island somewhere.