Rudi offers an excellent approach.

I don't know if you can get a LOT of compensation, but you should get something.

Write you letter outlining exactly what happened. Mention your status (1K, right?) and how long you've been with United. Enclose copies of your ORIGINAL itinerary and see what happens.

After about 3-4 weeks... call Mileage Plus and see what happens.

A few miles, maybe even a travel certificate.
It's something. CATMAN