I just rebooked a ticket via live chat and wanted to offer these specific words...MISMATCH FARE, EXCEPTION. We are 2pp biz flex plus ek771CPT to ek215LAX. 215 has not been flying but 225 to SFO has been so I wanted to get moved to 225. live chat said I cannot do that as there are no seats available in my fare class. I tried to offer some ideas about me paying for another fare class...perhaps that helped her think about this 'mismatch fare' exception. I think her point was one of the flights did not have any seats in my fare class...but somehow she sought an exception and we are rebooked. Also, live chat first said PLEASE HOLD, then said they were too buy to take my chat. I logged in 1 min later and the chat commenced just fine, no wait.

So if you hear from live chat you cannot be rebooked due to no seats in your fare class ask for the exception.