Please post a copy of message you received and no doubt experienced buyers and sellers will give you advice and information that will be of help.
Your post suggests there is a Charge back claim and cited reason is Unauthorised purchase.
This claim may not/ will not be from the buyer but from person whose Bank account was used to make the payment. As a victim of Fraud this person gets his money back from Banks and as you were the recipient of those funds eBay's managed payment provider may try to recover these from you. This would only happen if you have not followed all of eBay's policies.
There must be something else as this kind of case on it's own does not result in removal of a listing.
