This is an update on service from this post http://bad-service.livejournal.com/3274569.html
For reference, I sent the package (containing my pet fish) on April 16th, it was supposed to arrive on the 17th, and it did't actually get there until the 19th.
I eventually made it into the post office to process the refund a little over a week ago. Do they want to process the refund? Of course not! They say they don't guarantee shipping purchased online because "we can't say for certain when you shipped the package that day." So I pulled up the tracking which showed that I dropped off the package within half an hour of purchasing the shipping label. Then they say that, even though my receipt says "money back delivery guarantee by the 17th", according to their system, they had until the 20th to actually deliver it. "Guaranteed by the 17th" only meant that they'd get it statred by the 17th, not that it would be delivered. By the way, the 20th was a Sunday, so that made no sense.
In the end, I was getting nowhere with the troglodyte behind the counter, so I opened a dispute with my credit card. With any luck, their window to respond will pass due to the same beurocratic mess that got me there in the first place.
I find myself looking forward to the inevitable collapse of the entire federal postal service.