[quote name='SoulProphet']that is so true, paypal ruled on your behalf but still would not give you the money back then you can sue them for that.[/quote]
If I'm reading it properly, they refunded the money to the "buyer" and are trying to make the seller pay up for their (PayPal's) mistake, even though they sided with the seller.
That is ridiculous. I'd try contacting PP again and try to get some resolution. Make sure you keep EVERYTHING, especially the communications of them saying the dispute was found in your favor. If need be (but only as an extreme last resort), threaten legal action. You have, by their own admission, proof that they made an error, but are trying to put it on you to pay for said error.