I know exactly how you feel; my last TC AC was at one of the MC firms and still cannot comprehend how I failed it, especially since I had put lots of effort into it. Unfortunately, sometimes it happens that despite our prep, the interviewing process is, eventually, subjective - apart from all the "objective" assessment sessions they have. The truth is, and excuse me if someone disagrees with my opinion, a person can simply not like the interviewee. We are humans, and, unfortunately, that can put us down. Some people like me, some do not.
The only thing you can do right now is to keep your head up. Many people failed in the early stages of our age. It's normal. Some are lucky enough to get it at first shot, some aren't. It's a numbers game too. Do not forget that it is an incredibly difficult profession to get into. As Dan said - getting 4 ACs is a great achievement.
Relax, focus on your priorities, and start from scratch once more!
PS: what's meant to be. Trust me, this mindset makes your life easier. Good luck 
