Did you open a return case through Ebay?
If you buy from an Ebay business seller, they have to accept returns.
If you send an item back because it is the wrong size, you do have to pay so the seller has to provide their address but not necessarily a label.
You must use a tracked method and add tracking to the case.
Then, the seller has to refund you within 48 hours of tracking showing they have the item back.
If they don't, you go back to the case and ask Ebay to step in.
What went wrong with your return?
"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)