Hi Sebastian,
I appreciate what happened to you was intimidating and upsetting, but something still doesn't add up with your story.
I've personally never heard of anyone upgraded without a new boarding pass and seat assignment issued (or at least the new seat assignment written onto the boarding pass), regardless of what ticket and receipt you have.
Do you feel that you personally could have handled the situation any differently? What outcome do you see from the situation now? How better do you think CX could have dealt with your situation?