I'm so sorry to hear. I would contact the seller and see if you can get a refund I don't know what their return policy states otherwise I would file a claim with paypal. My sister bought a bag using my ebay id and it ended up being fake and I contacted the seller first and luckily the seller was really nice and willing to work with me and I was able to return it and get her money back. However, I know that is rare. If she refuses file a claim with paypal and you can always contact your credit card company too and put a claim in with them since the item is fake and try to get a chargeback.
You just have to be really careful with ebay. There are some authentic stuff out there and its a great place to find those rare or past season pieces. Otherwise, for current bags it really is worth the money and peace of mind imo to purchase it directly from the designer's store or dept. store. I really, really hope everything works out and you get your money back.