Ebay is rife with this activity, and it's horrible.
Did the seller post a picture of a geniune Estwing hammer? If so, that may help your claim. If you can demonstrate that you did not receive the product specified. Otherwise, Paypal may require you to prove that the hammer is counterfeit. As tool people we may consider it obvious, but it might not be so obvious to non-tool people. It might be beneficial to reach out to Estwing.
Also, bear in mind that however unlikely, it is possible that the seller was unaware that they sold a counterfeit product. Give the seller a chance to make it right, which it sounds like you may have already done.
Persistence and calm is the best tack, here.
Good luck.