At risk of tiresomely repeating myself, set up a payment plan. DO NOT overpromise yourself. Be sure to set up something you will find reasonable and be able to keep up with. You could pay your attorney to look at this, but what would it accomplish? They are doing it just like they do it. You were overpaid. They want their money back with penalties. Make a good faith effort to give them back their money. End of issue.