Why am I getting charged every month

Start with this link - How to cancel a subscription from Apple

How to cancel a subscription on your iPhone, iPad, or iPod touch

1. Open the Settings app. 
2. Tap your name. 
3. Tap Subscriptions.
4. 
5. 
   
6. Tap the subscription that you want to manage. Don't see the subscription that you're looking for?
7. Tap Cancel Subscription. (Or if you want to cancel Apple One but keep some subscriptions, tap Choose Individual Services.) If you don’t see Cancel, the subscription is already canceled and won't renew.

Then go to this link - Subscriptions and Purchases