I think the config setting "allow subscriptions" only controls whether users can edit their subscriptions, and does not affect existing subscriptions.
If you want to completely stop subscriptions from being emailed, you can either remove (or comment out) the cron table entry for the subscription script, or you can empty (delete all rows from) the w3t_Subscribe table.
If you only want to stop subscriptions for that one email address, you could examine the w3t_Subscribe table to see who that is, and then delete the applicable rows.
If you'd like personal assistance with this, please PM me.