Only eBay have access to your account and can see any restriction and be able to advise you further. At a guess, because of non activity on your selling account for a very long time, they need verification from you that you are the account holder trying to sell, and not a hacker accessing a dormant account.
Lines open in about half an hour.
Contact them this way.
https://www.ebay.co.uk/help/contact_us?id=4814&st=10
The contact links can be found on the left on that page.
Lines open today between 8 a.m. and 10 p.m.
