You must be logged in under the exact same username account that registered any blog who is the Admin of the blog and who purchased the upgrade to access it.
Clicking this link should display all your blogs registered under the same username, including the hidden ones: https://dashboard.wordpress.com/wp-admin/index.php?page=my-blogs&show=hidden
If you do not see the blog here http://en.support.wordpress.com/my-blogs/ then
follow this guide > http://en.support.wordpress.com/my-blogs/#my-blogs-dashboard-visibility
If you have lost your log-in information you can visit https://en.wordpress.com/wp-login.php?action=lostpassword If required click the "Need More Help" link and complete the form for account recovery.
Note that you can disable auto-renew Dashboard > Store > My Upgrades > Disable auto-renew