The 24 hour rule doesn't apply to award flights, I don't think.
But, this is ridiculous. They should give you your money back. They should have given it to you without re-issuing the tickets. They collected it for someone else, that someone else returned it to them. They have to return it to you; they have absolutely no right to keep that money. It's not theirs. Send them a letter (not an email or a phone call) and request it.
If you don't get anywhere, file a complaint with the DOT.