Steam has a full subscription management system wrapped up in their account details page. From here you can edit your payment method, cancel a subscription and see other billing details.
Here is a collection of details for the various features of Steam’s Recurring Subscriptions. If you purchased Patron through Steam, it automatically registered you to a recurring subscription. In order to cancel, you’ll need to visit your Account Details.
Any other questions about your account or any active subscriptions should be directed to Steam.