You might want to check with www.hud.gov for help. Your Realtor should also be able to give you advice. Florida has a ton of homes on the market, the lender may not want to add to that problem.
The promissory note is usually not secured by real property. You might want to talk with an attorney regarding your options. Depending upon the situation you might see if the buyers are willing to pay part of the promissory note.