To cancel all future charges, you may unsubscribe from our services. Please follow the guides below: https://support.apple.com/en-us/HT202039#subscriptions
Open the Settings app.
Tap your name.
Tap Subscriptions.
Tap the Invoice Maker icon.
Tap Cancel Subscription. The subscription is canceled and won't renew if you don't see the Cancel Subscription button.
Important: Simply deleting Invoice Maker from your device won't cancel your subscription.