Security Options

I believe has accessed my email account.  I have been trying to get into the security options to remove the secondary email address and change my security information.  I am prompted to enter a seven digit code.  I have requested an email be sent to the account listed in the security section, yet I never receive this email. I know that that account had also been accessed by someone.  Your customer support helped me get the password reset for the account but the security options is still an issue.  Please advise.

Thank you