Tough spot... the person giving the gift is technically not a party to the transaction and can't be required to give anything.
They screwed up and their post closing audit probably showed that they neglected to ask for complete documentation.
FHA guideline at
HUD Homeownership Center Reference Guide Gift Funds
They're asking for something that doesn't exist... you have to tell them and and say "what now?". Talk to the attorney that closed the loan for you, I think they'll have a tough time calling the loan, the lender is in trouble more than you are on this one.
They're probably going to want to refinance you asap on this one. If that's the case, they should do it at no charge to you and at a rate that doesn't exceed your current rate.