So what was the reason you failed twice? You allude to the fact that you don't interview well, but was that the reason you missed out, or was it another part of the assessment? If it was the interview, which part, because my interview was a bit like a chat in the pub? The lady that interviewed me reckoned her job was great, because she got to learn all about other people's jobs.
If you're the kind of person that doesn't communicate well, then guess what, you're not going to become an ATC, because that's what the job is.