USPS lost phone during upgrade

I upgraded my phone back in October and sent the old one back to Assurant with the prepaid label. It got to Texas, bounced around a couple days and it’s been missing since 10/21. I submitted a missing mail request but haven’t gotten any feedback yet. Not sure what the next steps are. The credit was for $700 so it’s not an insignificant amount. I contacted customer service over the phone but it was by far the rudest rep I’ve ever dealt with in my life.