Happened to me as well while on my honeymoon
I had booked my return honeymoon flight (HKT-BKK-PEK-IAH) with my father's air miles, and on the first day of my honeymoon my father forwarded me that same email from United in Chinese. I was supposed to be on Air China (first class) from PEK to IAH. Upon further investigation, I found that we did not have a return flight and had been cancelled. I called united and they proceeded to berate me about how I had to have cancelled it myself and that I had to figure it out because I had done this to myself. The lady even gave me the exact time, which happened to be when I over the ocean mid-flight with no access to wifi. Moreover, there was no record of the required $200 cancellation fee, as I have no status with United.
Only after my father yelled at United for over an hour did they attempt to provide me and my husband seats, and they were only able to accommodate us with some business and some economy seats; however, they were still charging us the same miles that we originally had booked first class seats with.
I was very upset with how United handled this situation. Whatever happened to customer service.