Both the monthly and annual subscriptions are automatically renewed at the end of each contracted cycle. With the renewal, the contracted records are updated, not being cumulative those of the previous month that have not been spent. If you register for example on November 15, the next billing cycle will be activated on December 15.
For your cancellation, you just have to go within your account profile to “settings”–>”subscription”—>”cancel subscription”. At least 24 hours before the renewal of the new cycle.