I order a textbook end of last month and the seller send the book the next day but I still haven't received the textbook yet. When I contracted the seller he gave me the tracking number saying that it was delivery on February 2nd but I never got it and when I told that to the seller, he told me he couldn't doing anything about that and maybe I should go to the post office and ask them what happen. When I went to the post office, they told that the tracking number said they delivery so they must have delivery but I told them I never got it but they told me they couldn't do anything about that. So, now what do I? Should I contract the seller ask for my money back or what?

Since this was an order through Amazon perhaps you can get help there?

Maybe it was delivered to your neighbor?   ask around.  Then go back to the PO and MAKE them research it.

I think one of you needs to file a lost book claim with the PO.  Sounds like it was misdelivered.

You can file a claim through Amazon's A-Z guarantee, if the seller won't or can't help you. Just because it shows delivered doesn't prove that you received it. If you used a credit card to purchase the textbook, you can dispute the charge, but I'd go through Amazon's A-Z first.