It is your responsibility to get the item back.
You will have to either provide a postage label or book and pay for a courier or arrange with the buyer to go and collect the item.
Once you have it back, you should refund and the case will close.
if you don't arrange to get the item back, the buyer can ask Ebay to step in after 3 days.
If this happens, Ebay will probably refund the buyer from your funds and tell them to keep the item so you do need to be pro-active.
"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)