You should send the item back.
Although Ebay may say there is no need to return an item when they step in and refund, most sellers still feel they have a right to have the unwanted item returned.
Personally, I would ask the seller for a label - they can supply one through Ebay - and then send the item back.
Ebay may have said there is no need to return the item but the small claims court (if it gets that far) may see it differently. And it should get the seller off your back.
"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)