You can cancel a subscription made to any Model, at any time, so you will not be charged anymore, by logging into your Membershyp account and going to "My subscriptions".
There, go to "Active", find the subscription you want to cancel and click on the "Action" button, as you can see in the picture below.
You will still have the "ON" status for the remaining days of that subscription but by pressing on "Cancel subscription", it will stop that subscription from being renewed again, so your credit card will not be charged anymore.
After the subscription's period expires, the model will remove you from the social account you subscribed to (Snapchat, Kik, Instagram, WhatsApp).
If you ever wish to subscribe again to the same model, just feel free do it :)