If someone beyond the postal service put something in your mail box, this is against federal postal regulations. Consult an attorney for this.
As for your sheriff sale concern, then one of a few things can happen. Somehow, pay the balance of the loan getting the bank off your back. Get the courts to stay the sale, they will have the requirements for this at the court house. Get with the Obama administration at http://www.whitehouse.gov/blog/09/02/18/Help-for-homeowners/
to see if there is anything they can do.
If there is nothing which can be done, then the sale will go on and you will lose your home.
Hope that helps,
Terrence Charest, e-ProÂ®
Century 21 Associates
905 Easton Road
Willow Grove, PA 19090
Cell (Preferred): 877.614.1494
â€œCentury 21 is the number one franchise site on the Internetâ€