If there was availability in U class, the call to the reservations number would have been able to get the rebookign done.
If U class was not available, then just take the flight as booked
You got randomly selected for screening - that's life
If same day change is available, that can be done online
I take it that you don't like people that you travel with if you actively avoid letting them know when they may be entitled to compensation and just go and claim your own?