Guest purchases (not completely signed in)  will not appear on your eBay account summary --- instead search here > 

Using a PC/Laptop, --- see if you can find the email  Guest order Transaction number details using the  Blue button in the link below --- Case options within 30 days from sale are there if needed > 

https://www.ebay.co.uk/help/buying/returns-items-not-received-refunds-buyers/returning-item/returnin...

https://pages.ebay.co.uk/ebay-money-back-guarantee/