Why is my credit card being used by iTunes ?

We are fellow users, we won't know what you (or anybody who has access to your accounts/devices/comptuers) are buying on your account(s), if you haven't already done so check via your computer's iTunes : See your purchase history in the iTunes Store on a Mac or PC - Apple Support

To see if you can remove the card, log into your account(s) and see if you get the 'none' option : Change or remove your Apple ID payment information - Apple Support

Log into your account and you can manage your payment method there. Be aware that without a valid payment method you will not be able to update your apps, or even download free ones.

https://www.apple.com/support/appleid/manage-account/

Be aware that without a valid payment method you will not be able to update your apps, or even download free ones.

You should be able to (as long as money isn't owed), it's only if you want to download something paid-for that you need a payment method or balance on the account.