as above, only extra i can add is you must wait 15 working days after delivery was due (10 for Special), so i’d ask the buyer to raise an ebay dispute and tell them you will refund once that time has passed and after you’ve emailed them to confirm still no receipt..
stick to the rules, rather than refund the buyer immediately as many buyers will try it on (ie receive and not repay any refund)..
i had a buyer claim my parcel hadn’t arrived, I’d entered an incorrect tracking reference on ebay,
i spotted it, amended the tracking number and it was clear the bloke had signed for the trainers 2 days after posting them. the scumbag