Contact eBay Customer Services they can explain why you are locked out from making changes.
At a guess, as you are selling all Brand New items and some in quantities of more than one, they may wish you to switch your Private account to a Business one, before being ablle to proceed with your account.
A Private account is for someone selling their unwanted second hand items.
The easiest and quickest way to contact Customer Services is through this link, for a Call Back .
https://www.ebay.co.uk/help/eua?id=5275&mkevt=1&mkpid
On weekdays lines open between 8 a.m. and 10 p.m. - 6 p.m.
Weekends lines open between 9 a.m. to 6p.m.
@khaiyeenow
