Well, sorry to hear of the shipping problem but I am not surprised. This is why I hesitate to ship fish from "cheap" carriers and prefer to pick up my fish directly. Yes, it does limit some things to where I am but it eliminates these kinds of issues....mostly.
It's all part of the "game" unfortunately.
I've had boxes opened, boxes lost, fish stolen out of boxes all from "reputable" shippers so nothing is guaranteed, especially when you have to mark the outside of the box with the contents.
For what it's worth, this is why fish are so expensive in the stores. They don't use the USPS for shipping so the costs of things are much higher but the rewards( actually having fish to sell) are higher as well.
As the expression goes, "It's all fun and games until somebody gets hurt." That usually ends up being the shipper and the fish.
Sorry to be a downer on a Monday morning.