Share 'post office recourse?'

So I sent a huge order to Microcosm and allthey got in the mail a month and a half later was our shipping label stapled to a letter. Apparently the empty wrapper was found in the mail, so they sent Microcosm what was left. This really sucks as it means I'm taking a hit of hundreds of dollars. Has anyone else been through this? Is there any recourse for me with the post office? I should mention I'…