If you forgot your Apple ID - https://support.apple.com/HT201354
"You’ve come to the right place to reset a forgotten password, unlock your account, or recover an Apple ID." - http://iforgot.apple.com/
What to do after [or before] you change your Apple ID email address or password - https://support.apple.com/HT204071
If you still need help:
Contact Apple for help with Apple ID account security - https://support.apple.com/HT204169 "This article provides country-specific Apple Support contact information for customers seeking help with their Apple ID password or other security-related issues."
Apple may remove a lock if you can provide sufficient evidence of valid ownership such as providing the original (i.e., when the item was sold to the first owner) sales receipt, preferably one with your name on it. You must take the device to an Apple Store along with required documentation. There is apparently no set policy (I asked at an Apple Store) and a store may simply refuse, particularly if they are not satisfied you have proven ownership by provenance.