If you received it less than 30 days ago, you can open a return case through Ebay.
However, if it is outside of the 30 days allowed by the Money Back Guarantee, you will have to start a chargeback with your payment provider. I would guess it is outside of that period as it was a Christmas gift.
How did you pay?
"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)