The only thing unfair is the way that message is written. The claim the item is 'not authentic' is not explaining the true issue here.
High brand items are protected by Vero Regulations and policies. It was the brand owner, not eBay who asked for the removal of your item.
There are so many fakes of high brand items and impossible to check authenticty for online items, even receipts can be faked, I know, my work took me to the Far East for decades , and fake receipts made there, are impossible to tell from the real deal.
You may well see identical items listed, the site is massive over 7 billion + listings on at any one time, so not possible to check every listing, and some slip the net and become listed.
Your item has been reported do not relist it, you would face serious selling restrictions.
You can read about Vero's policies from a link at the bottom of most eBay pages. or from the link here:
https://www.ebay.co.uk/help/policies/listing-policies/selling-policies/intellectual-property-vero-pr....
