If 30 days has passed the item's last estimated date for delivery then you cannot open any other case for that item with eBay.
This now will be between you and the seller to resolve.
You could try and turn to your payment provider see if you are covered with them, for any refund.
Or, if you purchased an item from a registered UK business who offered a warranty / guarantee and is now not upholding this, then you'd need to turn to Citizens Advice if you wish to pursue this further.