OK its me , but I dont see why the OP should get any miles back.Since they arrived at the Gate after T-15 CO gave their seats away figuring they wouldnt make the flight. Had CO not given them away and the seats went out empty plenty of people would be complaining 'Why did CO allow a flight to go out with empty FC seats'.
Had the ONT-IAH flight also for some reason not been in FC then maybe something could have been done, but once they flew the ONT-IAH segment that should close the case.
doesnt hurt for the OP to try and get something but I wouldnt expect much, especially not 25k as a poster mentioned above.