Why am I being charged for free apps

Are you sure you are actually being charged? That is, did you verify with your bank/credit card statement that this "free" app was charged to your account. Apple requires that you have a credit card "on file" to purchase apps from the Apple App Store, whether or not, they are free ... but the free ones should not appear as purchase debit on your account.

Slight correction: Apple does not require a credit card for free apps:

Create or use an Apple ID without a payment method - Apple Support

And payments can be made with Apple gift cards; without a credit card:

Redeem your App Store & iTunes Gift Card - Apple Support

Greenkaderli1: there are also many scams claiming bogus purchases:

Recognize and avoid phishing messages, phony support calls, and other scams - Apple Support

Greenkaderli1 wrote:

Why am I being charged for free apps

You aren't.

Thanks for the corrections/clarifications!