IANAL, but here is my advice:
File an eBay complaint for both sellers claiming the item was not received. I believe this is acceptable since both sellers can not clearly identify that it was their envelope that you received. If you're lucky, you'll get your money back from both.
p.s. In the future, when purchasing things from any place you suspect has tons of questionable sellers, try one or more of the following:
*. Separate out your purchases from China such that you only have one package in flight at a time.
*. Provide different shipping addresses to each item you purchase.
*. Ask each seller to put some unique identifier on the outside of the package (such as a name, word, or number - like a purchase order number).
*. When checking out, ask for a return address to be emailed to you before the package is sent (in case you need to return it), and ask that they write this same return address on the outside of the package, or on a piece of paper to be placed inside the package.