You will probably have to accept the return and provide a return label.
However, before you do this, message the buyer and ask them (politely) if they have got you confused with a different seller because the picture they have provided is not the item you sold them.
"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)