ISO info! Paid, delivered, never received. Help!

I bought this for $83 and was super excited to purchase, as it was the one I’ve been dying to have. It was a bday gift to myself for my struggle, hard work, and dedication. It was marked delivered yet I never received it. This is the 2nd time this has happened and it’s so upsetting. Post office needs the tracking number but I can’t find it. I don’t use this site enough and seller isn’t responding. Can someone help me? Isn’t there something I can do?