It's not clear what "virtual property" you're referring to, but it doesn't sound like your attempted sale was legal. Infringement doesn't require a sale, so whether or not you made a sale is not determinative, although it may impact how much you damaged the owner.
Only lawful buyers from the copyright owner get the benefit of the first sale doctrine and can dispose of the copy they've bought. It sounds like the work you tried to sell infringed on the actual owner's rights anyway, since the work was not a lawful or unlawful copy but some (illegal) derivative work.
You should make sure the company has a proper copyright registration to the work they claim you infringed, then make the best deal you can.
Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.