Don't close the return.
The seller can either provide a label, get the item back, and refund you or they can refund you without you sending the item back.
They don't need you to close the return to do either of those things.
Refuse the partial refund and wait for a label or a full refund.
If the seller doesn't refund you or provide a label, you can go back to the case and ask Ebay to step in.
Obviously you can't do that if you have closed the case.
"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)