I never had a payment declined so I'm a bit confused about this story.
In any event, you have a contract with FN and the guy has a contract with FN. FN are the middleman. That's why I'm always happy to see account/card jobs because, as far as I'm concerned, I'm getting paid regardless of whether FN does. If there is no money in the guy's bank account, that's FN's problem, not mine. He gives FN the money and they take their cut before passing it on to us. IMHO, FN owe you the money now.
I'd still report it to the Guards as a matter of principle. Unless we appear on the Gardai stats, we'll just be ignored.