Stuff happens, and packages are mis-delivered often enough that I wouldn't call it rare. In this case, the seller has acknowledged receiving it back, so there's no real dispute for ebay to enter (yet). I'm sure that since the seller willingly admitted having it, the only issue is who pays the expense of shipping anew.

If I were the seller, I'd offer you the option of a refund, less the postage paid, or resending if you paid the 2nd postage. After all the problem occurred at your end, either with the USPS or someone at your office complex.