Originally Posted by
garykung
Yes - because your ticket is not in control by UA. So the TA has to literally do everything for you, unless UA decides to take over.
Not entirely true. Having worked at a a company that used AmEx GBT there was no issues using the web or the phone to process a milage upgrade awards with co-pays days even weeks in advance of the flight. Hence, I would advise OP to hang up and call again (HUCA), perhaps with a North American agent (their number is 1-800-864-8331). If it's an IT glitch on UA's end they'll have the web team work on processing the upgrade.
One question for the OP : how are you getting this upgrade? Is this a buy-up offer, OLCI offer, milage upgrade award (with co-pay)? Depending on the nature of the OP there may be some truth to what the agent is saying.
Last and certainly not least, worst case scenario you can upgrade at the airport Kiosk. Offers from California to MEX seem to be at the $159 range during check-in
per my spreadsheet.
Safe Travels,
James