If you purchased a renewal or upgrade through the expiration notices from your Norton product, the days from your old subscription are automatically added to the new one. However if you purchased Norton another way, when you install the new Norton your old subscription days do not get added to the new subscription.
Under Services locate the Norton product that is installed.
If you do not see the Norton product with the subscription length you expect, you may need to sign into Norton using a different email address and password. If you see the correct Norton product, you can ignore the email.