Ruh roh! Your first plan of attack is to check with your neighbors, building managers, and other folks in the vicinity to see if they may have picked up the box.
If the address is accurate and you're not able to hunt down the box, I would try barking at your local post office to see if they might have it. Sometimes boxes accidentally get marked as "Delivered" even though they are waiting at the post office.
If you still can't sniff that darned box down, then pug. You should probably bark at email@example.com to see what we can do.