Hard to see a so good piece of equipment be broken like that but don't put more money to try to repair "multiple pieces" broken walls. Glued walls are solid in a corner assembly but not in a middle of a wall! Any honest plexiglas shop will tell you the same: they will have to redo all the walls. It is not UPS who will pay the repair!!
If UPS don't want to refund you, go directly to Paypal for a full immediate refund.
Save the parts that can be used as spairs for the next one you will found (soon!). Look for a pickup one near NYC (craiglist, WTB in photo forums), this will be the better way to not have it broken.