http://tortimeswqlzti2aqbjoieisne4ubyuoeiiugel2layyudcfrwln76qd.onion/bible/content/bible/shipping/non_arriving_packages/index.html
Politely (use sir/ma’am & please/thank-you) tell them that you’re experiencing issues with getting a package delivered, and were told to come down to this post office to pick it up because it’s sitting at this post office. If they ask what the issue is, say it was supposedly marked “Undeliverable”. They’ll ask for your ID, give it to them, and also give them the tracking number.