One year Verizon somehow lost both my wife's and my iPhone trade ins. We sent in our 6S's as trade ins for a 7 and a 7 Plus and neither were getting processed through the return center for some reason. I eventually discovered it when they started trying to bill me like $1600 for the remaining balance on the phones we sent back. It took me months to get it sorted out, after talking to several "managers". They even shut our phones off once because I refused to pay for phones I didn't have anymore.
When my wife traded in her 7 for an 8 and I traded my 7 Plus for an X, they only sent us return slips for one of the old phones, and it took me two phone calls to get them to understand what I needed, and then I had the same problem with the return of the 7--it had been sent back and received in the warehouse but nobody seemed to know what happened to it after that. It eventually showed up, but I never got the email saying they had it, which freaked me out.
SO......when I get emails like the one I got Saturday, I freak out. I think this year is the last straw--I just need to switch over to Apple's trade in program instead. I like Verizon's service and network speeds, but the trade in process sucks.