How do I cancel storage charges

Cancel by downgrading to the free 5GB plan. See instructions in: https://support.apple.com/en-us/HT207594

On your iPhone/iPad go to:

Settings -> Apple ID (Your Name) -> iCloud -> Manage Storage -> Change Storage Plan -> Downgrade Options. Under Choose Downgrades, select Free (5GB) and confirm.

Your current plan will be canceled, the date on which it will normally need to be renewed.