It may be that Audi only allow authorised business accounts to sell their parts on sites like Ebay.
Ebay tend to send a fairly generic email saying the item is 'counterfeit' even if it is genuine item but there is a Vero issue.
The best advice here is to sell it elsewhere.
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)