What happens if USPS looses my package.?

I ordered some lighters from amazon.com. The lighters were sold and shipped by a company called BURN wholesale. When I asked them why I haven't received my package, they provided me with the USPS tracking and it said delivered on the 13. On that same day, the mailman knocked on my door and personally gave some some other things I ordered online, not including the lighters. I don't know if USPS might have lost the package or just accidentally marked it delivered. I don't know what to do. Please help.