USPS Marked my package as delivered to my P.O. Box, but I never got it?

We have a P.O. Box and get a lot of over-sized packages with no problem. But every time we're sent any type of electronic device, it always disappears. The tracking will show "delivered" but there's no notice in our P.O. Box. We then go to the package will call window complaining about where the package is and they say, nothing is there and they don't know what happened. We asked them who scanned a package this past Friday at 12:25 PM as "delivered" and when we got to the post office at 4:20 PM, ONCE AGAIN no notice and the will call window doesn't have anything; can't tell us anything; and can't trace who scanned the packaged just a few hours ago, because "we have a lot of people working here." We have asked for a supervisor and filed a complaint to have a supervisor contact us, but a supervisor is NEVER available. We think the supervisor may be involved and this is theft by postal workers, because this is a locked P.O. Box and we ONLY have problems with expensive electronic devices being sent, like iPhones. What do you think? What should we do?

If you know someone who is a postal worker, we would love inside information.

A Supervisor or Manager should always be available. If the clerk is telling you that, it may be to keep them from hearing your concern. Not sure how you resolved the previous problems, but if you have the tracking printed out, your order info and other supporting information, I would Call and ask for the Station Manager or Postmaster. If you still do not get any follow up, call the US Postal Inspection Service. This is particularly the type of activity they are set up to investigate.