That's not a bad idea at all! I think I'll start adding those extra CYA layers you mentioned next time. I don't know why, but that's always terrified me, too.
Well, I had hopped online to view my account when I saw the huge $500+ charge. After collecting my jaw, I pulled up the scanned documents I kept and found the tracking number, which then led me to FedEx and proof Verizon had received it.
Long story short, I just this moment got off the phone with Cedric at Vzw who told me they received the phone and that despite the website showing the charge without a credit, the credit had indeed also been applied. So
according to Cedric I have a zero balance. Naturally I recorded the call and will wait and make sure all is as he says it is.
Loose ends: So the culprit appears to be my local FedEx Store, that, according to the tracking info, inexplicably held onto the package for a few
weekdays, returning the phone past the Vzw 10 day window and causing me to get dinged.