Seller is supposed to get item back first before refunding. When they refund upfront ebay assume they don't want the item back and do not supply a postage label.
Now the seller can only send a label outside of the ebay system, eg. buy from Royal Mail online and send you the QR code to take to your post office and they will print label for you.
But maybe they don't want it back. If they don't reply you don't have to do anything.