While sad to see customers go you are free cancel your plan and cease payments at anytime. The cancel process takes just a few seconds and includes steps for you to leave feedback and let us know if there is anything we can do to keep you (really, what can do for you?).
Cancellations are are immediate one you complete the process and you will lose any features related to your plan. That also means all but your stories will revert to a draft state and no long be publicly accessible.
Depending on your renewal period you may eligible for a refund, learn more about that here.