Their current ebay ads say 'Condition:New with defects' and 'These helmets sold by us on ebay are old stock which are in clearance or have minor blemishes.'
ebay's definition of the description 'New with defects. A brand-new, unused and unworn item with some kind of defect. Possible cosmetic imperfections range from natural colour variations to scuffs, cuts or nicks, and hanging threads or missing buttons that occasionally occur during the manufacturing or delivery process. Apparel may contain irregular or mismarked size tags. Item may be missing its original retail packaging materials (such as original box or bag). New factory seconds and/or new irregular items may fall into this category. The original tags may or may not be attached. See seller’s listing for full details and description of any imperfections.'
If your ad said the same then the description is accurate - it has some kind of defects.
If it said'only has a mark on the top' then you MIGHT have grounds for return as misdescribed.
Worth calling them, you never know!