eBay have very strict timelines when you open any case, under the 30 day MBG Money Back Guarantee policy see here:
https://pages.ebay.co.uk/ebay-money-back-guarantee/
For item not as described you return the item at the seller's expense add the tracking number into the case details and once shown delivered the seller has 48 hours to refund you.
If they don't, you Must escalate, ask eBay to step in and they'll force the refund.
If you did not escalate, with no activity the case times out and closes. You cannot open another case with eBay, but can turn to your payment provider for help now, with a refund.
@stuhan8