If you had previously suspended your account and just reactivated it, you may have been returned to a Free account. This is because accounts are not renewed while they are suspended, even if auto-renew was not deactivated.
Other reasons your account may not have been renewed include an expired credit card, cancelled credit card, or other error received from the credit card company. In most cases, you should have received an e-mail letting you know about the error. In these cases, you will need to re-subscribe to activate your subscription.