Typically, whenever you receive a product that has been damaged in the shipping and handling process you would merely contact the seller and either get a refund or a replacement. But, when you are dealing with a latex item the product (and in this case any masks you buy) may not actually be damaged at all. It all comes down to the unique properties of latex and how it is designed. What happens with the material is it will take the form of whatever it is pressed against. So, if it arrives at your doorstep and is deformed and distorted, it is probably just fine.
What you should do is remove it from the packaging and allow it to reform its shape. To speed up the process, you can take a low-heat item (such as a blow dryer on its lowest heat setting) to restore its shape.