Changed my email and now can't access my backup to change it, as I've forgotten old password

My Norton 360 won't let me set up my backup, I changed my email a few years ago and have forgotten the password I used,  how do I get it to accept my new email and password. Its keeps sending new temporary passwords to an email account I cannot access. Its driving me nuts to the point that when it comes time to renew I'll be picking another anti virus provider that doesn't make me crazy.