Agree with the above, the buyer doesn't have any grounds for returning the item (unless you stated you would accept a change of mind return after this amount of time, and I'm guessing that's not likely).
The listing would still be viewable on eBay, so it should be very easy to point out to them the fabric content was fully disclosed in the listing, and highlight whatever applicable points of your return policy there are (eg no returns, or the time limit for returns). You may want to suggest some alternatives, such as on-selling the garment - some buyers have been quite happy to do that as I've offered the full use of my description and images.
