Effectively. I just chatted with one of their reps. He said he understands my concern, but promises that if I am not refunded the $600 too, I can just contact them back and they'll sort that out quickly. Given how slow they have been to do anything, I asked him to just correct the email to include the full amount. He said he can't because the price I originally paid is all that can be reflected in this automated email.
I suspect their ERP system probably does have that restriction. But at the end of the day, it took me threatening to sue them just to get them to send me the shipping label. They were not interested in helping me at all. From word 1, it was sorry, the trade was declined. No further communication necessary, etc. Push, escalate, wait 30 mins, get a supervisor, then ok, maybe we can look into it and so on. I don't have time for this. I'll sell the Pixel 3 and cut my losses.