How to stop automatic payments?
How to stop automatic payments to iTunes
iPhone 12 Pro Max, iOS 14
If it is for a subscription, see: How to cancel a subscription from Apple - Apple Support
If for iCloud storage, cancel upgraded iCloud storage by downgrading to the free 5GB plan. See instructions in: Downgrade or cancel your iCloud storage plan - Apple Support
If that doesn't help, see each of the steps in the following instructions. They include information on contacting Apple Support if the other steps don't help: If you see 'apple.com/bill' on your billing statement - Apple Support