A Guest purchase when not completely signed in will not show in your eBay summary --- > 

Find the email  Guest order Transaction number details in the link below --- Case options within 30 days from sale are there > 

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/