Originally Posted by
whipwhitaker
....
COC obligations go both ways, and the airline cannot arbitrarily cancel your ticket after one of their employees made a change to it. ...
While I would agree for the first time, but once cautioned by UA and continuing knowing it is a problem (as it appears the OP has done) puts this in a different light IMO,
Based on other incidents, UA does do these extreme remedies unless there have been multiple events. And perhaps the first time the itin was canceled should have been sufficient notice it might be best to stop.