cancelling an old email

I am currently an xfinity internet subscriber. I also have an old email address from a previous subscription that I am no longer using. I would like my old email to be cancelled. The problem is, if I login to my old email it resets the 9 month inactivity period. I want the email cancelled immediately so that senders realize that account is no longer being utilized. The 9 month period is too long for me to wait while emails to my old address are being ignored. Please help me to cancel my old email address today.