(FINAL UPDATE)! UNITED LET SOMEONE FLY UNDER MY TICKET.

Here is the link to the OP: https://www.reddit.com/r/unitedairlines/comments/1hm5u3s/united_let_someone_fly_using_my_ticket/

Update: After two weeks of being dismissed and blamed by United Airlines, I finally got answers, thanks to the Port Authority Police. They investigated, reviewed airport footage, and found that a gate agent rebooked someone with only the same last name as me onto my reservation after they missed their morning flight, and printed them a physical boarding pass. No other details—like first name or ID—were cross-checked. This person boarded using my ticket and even checked a bag under my reservation with a credit card that wasn’t mine.

United refused to investigate initially, claiming this was my fault. I felt belittled throughout the process, even though this was a clear mistake on their part. The detective 100% told me this was a fault of United (not tsa or anything). The fact that such a breach was handled so poorly is shameful. They eventually offered me flight credit ONLY AFTER THEY GOT CAUGHT, but It'll take a lot more than what they offered for what they put me through around christmas. They had respond to me saying: "we investigated and found the problem but we cant provide any details", yeah well you don't have to because the detective gave me the police report with all the information. Its hilarious how quick they emailed me back after hanging up with the detective who told me he called them. Does anyone know if I can push for direct cash compensation instead?

To anyone who finds themselves in a similar situation: do not give up. I was surprised as usually reddit has all the answers but I couldn't find nothing like my situation. Consider this a warning if it happens to you: Filing a police report was the best decision I made. Without the Port Authority Police, this would have been swept under the rug. United should be held fully accountable.