If you have an NS Flex Weekend Vrij subscription, then you can easily change it to NS Flex Basis (= NS Flex without subscription) yourself in Mijn NS (the website, not the app) if you've had the subscription for at least a month. The change will take effect immediately. You can continue to use the card to travel on invoice, but will pay the full fare for all future journeys. Until you decide to take a subscription again, of course.

If you've had the subscription for a long time and don’t have the NS Flex variant, please read the information on this page for instructions on how to cancel.