Part of the problem is United waiting until the very last minute to upgrade people. It has gotten ridiculous. I was flying from Europe last week and I boarded since it didn't look like my upgrade was going to go through. 5 minutes before departure a woman comes on the plane with my same coach seat. It took another 10 minutes before they figured out I had been upgraded (and my phone didn't say that I had).

The OP issue is 100% United's fault. I recommend asking for a supervisor and they will credit the GPU back.