Receiving Apple ID security notifications for an email I cannot access

I have two email accounts but only one is registered in my apple account. I get daily emails from apple telling from the second, non-registered account telling me that I have changed my birthday, set up two factor authorization, etc. However, I cannot get into my account using this email (when it sends the two -factor authorization it is not to my phone). I have changed both the email account's password and my apple password but this keeps happening. How can I make sure there is no apple account associated with this email when I can't use this email to get into the associated account?