Trade in disaster

My device was mailed within the required window using Xfinity's prepaid label. USPS tracking explicitly shows 'In Transit.' Xfinity closed my ticket and is refusing my promo credit until it is received. Because Xfinity owns the corporate shipping label, the shipping risk is yours. I need a Tier 3 Mobile Escalations Specialist to manually review this tracking data and apply my credit. I can't submit a claim with USPS because I am not the sender, Assurant is. I typed my IMEI into assurants website and the phones appear registered to new phone numbers so I know they were stolen. My USPS tracking has stopped updating since July 2nd in Philadelphia. I have done my part and mailed two phones in (and have proof) and am being denied my trade in value because it was not received by assurant (because it was stolen in transit!) I am beyond frustrated after being an xfinity customer for over a decade.