This is not legal advice. Michigan has both judicial and non-judicial foreclosures and the right to redeem. You need to be at the court house the minute they open on Monday and pull everything on file regarding the foreclosure and give it to whoever you are working with at NACA. NACA members are typically lawyers. Hopefully the sale was judicial and has not yet been ratified by the court.
NACA will need to file something based on the fact that negotiations were underway and an agreement was near. If nothing else they were dealing in bad faith by proceeding with the foreclosure, which could be a cause of action to put the breaks on the sale. More then likely they bought the property back rather then have sold it to a third party. Hopefully your NACA contact has the modification process well documented.
HANDY LINK: http://www.foreclosurelaw.org/Michigan_Foreclosure_Law.htm