Sellers can only close returns that have used a "change of mind" reason, such as doesn't fit, or if it was started beyond the 30 day deadline.
On rare occasions ebay have been known to reopen closed cases so it is worth asking. You can use callback on here:
https://www.ebay.co.uk/help/eua?id=5275&mkevt=1&mkpid
If not try contacting your payment provider and ask about a refund or chargeback.
@saxmurphy