All you can do is message the buyer again and offer to provide postage so they can return the item to you if they don't want it.
You can't reverse the refund or send them a new invoice through Ebay.
You are dependent on the buyer's honesty.
"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)
