You're caught at the unfortunate confluence of four circumstances:
1. Flight disruptions at EWR due primarily to weather and inadequate air traffic control staffing and overall airline dysfunction;
2. Extremely heavy flight loads to Europe;
3. Inexperienced UA phone agents who are not empowered to provide meaningful assistance;
4. UA selling a cabin (premium economy) that it does not offer on all widebody aircraft, and then totally failing to take care of the passengers that are affected by cancels and/or aircraft swaps.

It's the last two of these, particularly the last, that are fully within UA's control, and they are behaving despicably in taking passengers' money and then not providing the product that was paid for.

I encourage all who have been victimized to complain to DOT.