How do i cancel my plan?

you must cancel your subscription within the refund period.  make sure you're aware of the cancellation terms by selecting your plan type (at the top of the page here), https://helpx.adobe.com/manage-account/using/creative-cloud-subscription-terms.html 

for info on how to cancel your subscription, this page describes the few steps involved, https://helpx.adobe.com/manage-account/using/cancel-subscription.html

if you want to cancel but are unable to follow the steps described in the "how to cancel page", you probably have a payment error that you need to repair before cancellation is allowed, https://helpx.adobe.com/manage-account/kb/fix-failed-missed-payment.html