A Petition against USPS, do not respond for a package that contains my original school & college certificates.

On April 18, 2014, I send some documents that contains my original school and college certificates to the "Institute for International Credentials Evaluation Services, Fresno, California 93740." I choose a Priority Mail 3-Day service, insured and request Adult Signature confirmation at the time of delivery. When I track the item on April 22, 2014, it shows that, "Your item departed our FRESNO, CA 93706 sort facility on April 22, 2014 at 5:26 am. No further information is available for this item." I try to contact 3 post offices and went to the main post office to share my concern. But they answered.."don't know anything". Atlast the postal service gave me Consumer Affairs contact no. When I call them, they promise me a call back. But unfortunately, nobody give me a call back... Pls help