All I can advise is to change your email address with the link below to your Personal Information,  and use a laptop / PC to do this,  not the app or mobile browser.  Chrome works well with eBay.

https://accountsettings.ebay.co.uk/profile

If there are still issues in registering your new email contact CS who have access to your account and can help you futher here.

Contact them with link below preferably at 8 a.m. when there's more chance of Dublin replying.

https://www.ebay.co.uk/help/eua?id=5190

@roberts_54