Finding Lost USPS Mail Without a Tracking Number?

I'm from India and I had cleared my CCNA exam, but the certificate has to be sent from United States. Cisco is telling that my certificate has already been sent to me, but I had not received it yet.

They have not given me any receipt number to track my certificate. So if any one knows how to get a receipt number I would appreciate your help. It was dispatched on the 16th of March 2011. It has been almost 4 months.

By guddu from India