Start the process now. PayPal will deal with it. It doesn't instantly give you your money back, PayPal contacts the seller and tells then a claim is being lobbied against them and they have a choice to either make it right or challenge it. They have to respond, and if you get no response, you can escalate it to a fraud claim and you will get your money back.
^^ This, just filing a claim does not hurt the seller. It makes them take notice that you are serious about getting something resolved and in most cases, motivates the seller to open communication with you. And as the last resort, if they still don't, you have a solid leg to stand on when it's time to complete the dispute.
(Btw short of an apocalypse, with smart phones etc, there is no way a seller should not contact you back within a 48 hour time frame.)
I sell stuff, just not shrimp.