Why can't I access my Google account?

Reaching my account through recovery email doesn’t work.
Trying to recover my account through my phone doesn’t work.
Entering various captchas (obscure letters) with at least 90% success doesn’t work.
Trying “forgot password” or “forgot email” is not working either.

Still ends up with saying that could not confirm that I’m the owner.
One thing they haven’t done though is asking me the security questions I made when signing up for the account.
This is 15 year old account.
It would be a real mess if I can’t get it back.
It’s not deleted because signing up with the same username, they say the username is unavailable.

Can somebody help. me on this?