Most sellers will not file. I had the PO tell me the seller had to file for the lost package. The seller told me it was on me to file.
You can file it yourself online. They aren't very helpful with claims in the office but it's fairly easy to do on the website. I still feel it's poor business practice for the seller to not help you with it. I have a small business and the couple of issues I've had with the post office I made right because I feel like if anyone should be shorted, it's me, not the customer.