USPS may have lost trade in - next steps

My trade in might be lost. I’ve initiated a lost mail search with the USPS, but how do I make sure that I get my trade in credit if the USPS can’t find the phone? Assurant didn’t purchase insurance, so the package only has $100 of coverage (USPS Ground Advantage) - it’s a $700 phone. The package was scanned in by USPS, so I can show that it was shipped by me.