I'm reaching out because I'm totally at a loss right now. I booked a flight from BOS to LHR through Expedia that is operated through Delta & Virgin Atlantic. (BOS->LHR virgin, LHR->BOS Delta). I want to pay for an upgrade to Economy Plus to London, and I've checked to see that seats are available.

Called virgin who told me I needed to call Delta who said I needed to call Expedia who said I needed to call Virgin again. Virgin is now saying I can upgrade the day of my flight but there's nothing they can do now.

What should I do and who should I go through? I'd love if Delta could upgrade me since my amex plat is with them, but I'll take anything at this point. Why am I getting so much push back?