Who I have the same questioned this topic

I attempted to trade in my iPhone XS Max on 4/7/20, and received my iPhone 11, which is the phone that I am currently using. I mailed out my trade-in device using the provided packaging and dropped it off at the post office. I never got a notification that it was scanned in, and just feel very lost and confused as to what to do?? Now, a billing cycle later, I’m seeing this HUGE $1,100 Verizon bill because my trade in wasn’t received. I clearly don’t have the phone in my possession, is my only option just to foot this $1,100 bill? Since my phone is technically missing/stolen would I be able to file a missing phone claim, get a replacement and send THAT phone in? I’ve seen other posts like mine, saying since there’s no proof that I dropped it off, I’m basically out of luck. Help me please!