Originally Posted by AXR64

I'm in the same situation except I'm flying Y. Called United and was told there was nothing they could do other than cancel and refund. I asked them to add a BKK-CNX segment on TG to my itinerary but they said they saw no availability. At first I found it hard to believe - I recall TG having about a dozen flights a day between BKK and CX. Looking further I saw that all those flights now are operated by ThaiSmile, TG's low cost subsidiary, and I assume seats on ThaiSmile are not bookable with UA miles. So I just booked a separate BKK-CNX flight on Thai VietJet for $51.