Welcome to Shopify Community. My name is Olivia and I work here.
I'd love to help you out today. Is this an app you downloaded from the Shopify App Store? If so, you can cease future billing by uninstalling the app in a few simple steps.
From your Shopify admin, go to Apps.
In the row of the app that you want to uninstall, click Delete.
In the message that appears, click Delete.
P.S. Once the app is uninstalled, it won't appear on future invoices after the app's existing billing cycle ends (remember app billing cycles are separate from subscription cycles). View upcoming bills by heading to Admin > Settings > Billing.
Let me know if any other questions come up.