Welcome to Flyertalk! Sounds like a potential customer customer response issue, along with a cancelled award ticket. A couple of questions:
1) Were you still planning to travel to Paris? If so, sounds like they have offered an alternative (flying through US instead of other European hubs? - need more details here). Have you contacted LH and see what alternate booking they have made for you?
2) It sounds like you may have encountered a frustrated agent, who couldn't figure out what solution would be acceptable to you. What would you like United to do for you when you called? Not to place the blame on you, but just call and vent without a proposed solution doesn't help anyone. Help the agent to help you.