Is it possible you've accidentally bought as guest or created another account without realising.
If you logged in accidentally using the "continue with Facebook/Google /apple" buttons it creates a new eBay account.
The account you've posted on here with was only created on the 1st April 2024.
Is it your only account?
Try logging in using a browser instead of the app as it could also be an app glitch.
Are your trainers visible on this help page?
https://www.ebay.co.uk/help/buying/returns-refunds/return-item-refund?id=4041
Here's a link to contact eBay customer services that bypasses the automated assistant during working hours.
https://www.ebay.co.uk/help/eua?id=5275&mkevt=1&mkpid