12-05-2021 3:21 PM
You can't postpone your case. The seller should refund you. The claim with RM is for themselves. You will be able to escalate your case after 3 working days then ebay will enforce the refund. If you allow it to expire you may get nothing from the seller.
Make sure that you escalate the claim at the earliest possible moment that you can. The 15th will soon be upon us!
"Royal Mail investigating" is meaningless. Either the seller can show delivery by tracking or he can not. That is all that will matter to eBay