That's pretty much par for course with the USPS. One of the selling points of UPS/FedEx is that they have actual proper customer service (at least for large accounts).
I know this because the tracking information a USPS clerk looked up for me showed the delivery person marking the package as delivered while being nowhere near the delivery address. In fact, nowhere near an address at all. It was marked as delivered to a street-intersection which houses a vacant field.
The USPS clerk acknowledged this, but said that because there were no other complaints about the delivery person that day, there was nothing they could do.
So it seems like USPS delivery people are literally allowed to steal one item of mail a day.
Parent agency: United States Postal Service