I have had a $19.99 chargeback with my Chase Marriott Bonv°y Visa every month since February 2020 (for a cancelled service), and that is indeed the procedure. I receive a temporary credit, and after the service provider fails to respond, the credit becomes permanent.

I have moved my household spend to my wife's card, and changed my statement date to the day before the "cancelled" service appears monthly, to simplify my monthly dispute.

As a reputable service provider, it is highly unlikely UA will persist in claiming the charge was valid after you have documented evidence of telling them you were not on the flight.