I wouldn't call them on the phone. I'd go to the post office and see a clerk in person. When I've had Priority Mail packages go missing, you can bring in your receipt, the white one, and they do have a way of tracking it, just at what points it was scanned, even if you don't have delivery confirmation or insurance. When I've done that, they usually have to go get a supervisor, because not all the clerks have access to the computer that can track it, but it can be tracked, even if no special services were purchased.