Personally, I would do nothing.
If Ebay identifies and closes a suspicious account, they let any involved sellers know, and tell you not to post the items or to contact the buyer.
I would relist the sold item as you can't post it. I assume you have not been paid so there is nothing else to do.
"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)
