Hi there,
Had an experience this morning that may help some and wanted to share.
I was on the receiving end of this problem - I ordered a package from overseas, and it was (and technically still is) stuck in the eternal loop of one of the USPS sorting facilities. Don't bother with the 800 number - you'll never talk to a real person through it.
After some hunting and talking to my local post office, I was able to get this phone number for a Routing Center near my area: 847-595-7350 (also, extension 7351 will work).
When you reach the real person on the line, ask for "In Plant Support." That (mercifully) also brought me to a real person. I was able to explain the situation of the package being "stuck" at the sorting facility, provided the tracking, and the representative was able to find the package in the system immediately. Turns out that the sender of the package did not include the ZIP code on my shipping address. Everything else was there - just not the ZIP.
The representative said that this often is why a package will go 'round and 'round a sorting facility - if the address that's scanned by the computer has no ZIP code, it will go through the facility for some time, then get forwarded to the ZIP Code Correction Facility. There, they have real people fix the ZIP, and then it will get sent out.
She said in some cases, if the address is garbled or illegible, then the package would get sent back to its destination. But, she said, that for both packages going out and coming into the USA, it's usually a postal/ZIP code thing that gets packages "stuck" like that.
While clearly I don't know all the Routing Center phone numbers, or if the one I've posted here will help anyone outside of Illinois, but I'm hoping that this info is helpful!!
Lots of Smiles,
Miyu-chan