For users of the iOS version:
Go to the App Store -> Click on your details (right corner) -> Click on your Apple ID -> "Subscriptions". Tap a subscription of Annie Baby Monitor and then tap "Cancel Subscription".
For users of Android version:
On your Android phone or tablet, open the Google Play Store (check to make sure you’re signed to the correct Google Account). Tap „Menu“ (your icon / profile photo in upper right corner), then tap „Payments and Subscriptions“ and choose „Subscriptions“. Select Annie Baby Monitor app, tap „Cancel subscription“ and follow the instructions.