If the refund hasn't been made yet, there should be a "Report a problem" link in your return case, use that to report that you've received a damaged item back. I believe that you can add a photo.
Once you've done that I'd also contact eBay and go over this with them. I’ve found that the easiest route to contact eBay Customer Services is via the link below, you can select to talk with them via live chat or request a call back:
https://www.ebay.co.uk/help/eua?id=5275&mkevt=1&mkpid