You are not subscribed to a premium plan and are on a free plan.
Paid plans are billed via your Google Play account.
Your paid plan will be automatically renewed. You can stop the auto-renewal at least 24 hours before the expiration date.
Paid plans are renewed between 24 hours prior to expiration and the end of the expiration period.
You can change your registration details or stop auto-renewal from the Google Play settings page after purchase.