(Reposting since friend's account was closed awhile back)
This requires little to no effort and is a little different from all the other ways people do it.
I discovered this method myself not long ago and have decided to share it with you guys.
Only things required:
Your alts to have been on the account
Previous email
Gamertag
Step 1: Call 1-800-4MY-XBOX
Step 2: You will need to say you believe your account has been compromised, your email says it hasn't been created or doesn't exist
Step 3: Ask if they can send a verification code to your previous alts on the account (first alts ever put on it, occasionally some after it) they will then send out a code to all the previous alts even if they are removed.
Step 4: They will now be in the account, you just simply ask what the email/phone number is. They will give it to you since you got them in.
Step 5: Ask if they can update your info on it, they will add a secondary email and whatever else you ask.
Step 6: Tell them to forward a password recovery to the advocacy team so you can get back in your account.
Step 7: Wait around 24-48 hours for your reset link.