Glad you sorted it. Sadly it looks like they're getting better at hacking accounts - when they hacked mine they didn't change the questions.
Weirdly Apple never gave me the option of using the serial numbers, they out and out said there was absolutely no way at all to unlock the account if I couldn't answer the questions correctly, which was a pain because I really struggled to remember what I put as the answers because I set up the account nearly a decade ago.
They initially went down this root asking me the questions but some of them i knew i would never choose like 'What's your fav childhood book?' Also the questions were coming up in Chinese so they figured the questions were changed. Apple said someone was able to get into my email account (yahoo) and managed to reset the account or managed to guess my security answers.
They also advised it was a good idea to use a rescue email so in the event of a hack you can reset the security questions yourself.