buyer requesting return on item as described

[rdmack]

I am not an experienced seller, but on rare occassion have sold items.  Our feedback score is 100% and have been a member for several years.  I put an item up for auction with buy it now option, for proactive plus hydrating cream, completely sealed and new, expiration date 6/15 which I noted twice in the listing, as well as listing twice no returns, and to please email if any questions. Buyer used the buy it now option, paid immediately, item was shipped next business day, and now buyer requests to return stating the item is expired.  I left positive feedback for buyer due to prompt payment, emailed buyer through ebay stating that I was sorry but I listed the specifics very clearly.  Received email from ebay minutes ago stating that I have 2 days to resolve.  I have never had to refute a case before, any advice?