The same thing happened to me a couple months ago. I called eBay right away and told them what the situation was before the refund came out of my account automatically. They suggested I contact the "buyer/returner" and try to work things out first and if that doesn't work, file a police report. I did wind up contacting the buyer and at first they seemed confused. (I was supposed to get a helmet back which they left negative feedback for already, but instead got a small box filled with women's receipts for phone purchases from Verizon and AT&T. It freaked me out since there was a lot of personal info there.)
After a few back and forth messages, I did finally get the helmet back.
It was a very weird situation but I think it worked out because I took the stance with him that we just got the wrong box.
Stay positive and things tend to work out better.
