iPhone trade ins were shipped back to Assurant but lost in the mail - how do I get my trade in value credited to my account?

I recently traded in an iPhone 11 and iPhone 13 to get iPhone 15s to upgrade both devices. I was given an offer of $200 for the iPhone 11 trade-in and $500 for the iPhone 13. I was sent pre-paid labels from Assurant to return the devices to Assurant for assessment in order to receive the credits on my Xfinity account. I shipped the phones in separate boxes with their respective prepaid labels on Sept 17, 2024. Both of the packages were lost by USPS. I filed service requests for both packages using the tracking numbers. USPS recommended I file an insurance claim for the lost parcels with phones inside. I spoke with USPS and am unable to file insurance claims with USPS because Assurant paid for the postage and is listed as both the sender and receiver of the packages. I also learned that Assurant only put $100 of insurance on each of the packages even though the phones are valued at $200 and $500. I am unable to file an insurance claim with Assurant since these phones no longer have an active cell number. I have spent HOURS upon HOURS trying to resolve this in conversation with Xfinity and USPS. How do I get my trade-in offer credits of $200 and $500 now that the USPS has lost the packages with devices inside and Assurant only placed $100 of insurance on each of the labels???