If you pay with Patreon

Premium account purchased with Patreon would be automatically purchased and prolonged at the first day of every month.

If you want to cancel your account prolongation please disable your reward on Patreon by this article: https://support.patreon.com/hc/en-us/articles/360005502572-How-do-I-cancel-my-membership- 
Note that you premium account would disabled at the end of purchased period.

If you pay with credit card (without Patreon)

Premium account is purchased for 1 month, and then you need to manually purchase premium again. We send you email when you account would deactivated.