If you haven't received them, open an Item Not Received (INR) case in the Resolution Centre.
If you have and they are not absolutely NOT legit, open a Significantly Not As Described (SNAD) case in the Resolution Centre.
The first step is to always Contact Your Seller but if that has not worked, go straight to a case. Escalate it as soon as is possible.
Don't accept an offer to replace from the seller. Unless you have a previous relationship with the seller and the item can be delivered with tracking within a week to 10 days, it often does not end well. Take your refund and try again.