Originally Posted by
WineCountryUA
Nowadays UA will many times catch irrop rebookings into a higher fare and give you the fare class you booked/purchased. Years ago you might have kept the irrops rebooked fare class, now it is more common for UA to catch this. Unfortunately, this was a risky thing to count on.
This. In my experience, they now catch it basically 100% of the time when my upgrade clears but nearly 0% when it doesn’t.
OP: Your best option is probably to contact customer care / MPSC and ask for them to honor what was printed on the receipt. I can’t promise it’ll be successful — ultimately, your earnings match what you originally paid for the flight — but there’s zero chance it’s going to change if you don’t ask.
Good luck!
PS: Keep in mind that one possible outcome of contacting them is that they remove your bonus miles for the IAH-SJU flight. So, if you’re of a mind to pay a buy-up offer, you might want to think about whether or not it’s worth the risk to ask.