You can cancel your subscription at any point to stop any future payments. To avoid being charged again at your renewal date (or at the end of your free trial period), be sure to cancel your subscription or trial at least 24 hours beforehand.
Check out Google Play's cancellation steps for more info on how to manage your subscription from your preferred device. If you have any trouble with these steps, please contact the Google Play support team for further assistance.
Hope this helps!