What to do in this **bleep**py situation?

[afveteran]

I recently sold an expensive school text book after I completed the course and the buyer promptly paid and I promptly shipped.  However, the USPS lost the package and the buyer filed a claim to which I'm forced to respond and I ended up refunding because I had no options, even though I had a tracking number.  So now a month and half has passed and the book finally appears delivered via the tracking number.  As you guessed, the buyer now has my book and their money back and it's too late for me to file a claim or do anything.  This transaction seems to have fallen into that abyss between the drivers seat and the console...

...the buyer won't respond and my hands are tied because ebay seems to favor the buyer over the people who make their silly auction site even work.  Any ideas on what can be done?