See -> If you can't make purchases or update apps, including free apps, you need to update your payment method or add a new one.
but I’m not trying to buy anything. So I added a card with no money then it charges me 29.93 dollars
See the following Apple articles:
Payment methods you can use with your Apple ID
Payment methods you can use with your Apple ID – Apple Support (UK)
Add money to your Apple ID balance
Add money to your Apple ID balance – Apple Support (UK)
What you can buy with your Apple Gift Card or Apple ID balance
What you can buy with your Apple Gift Card or Apple Account balance – Apple Support (UK)
then it charges me 29.93 dollars
See the following Apple articles:
View your purchase history for the App Store, iTunes Store, and other Apple media services
View your purchase history for the App Store, iTunes Store, and other Apple media services - Apple Support
How apps, content, and subscriptions from Apple are billed
How apps, content, and subscriptions from Apple are billed - Apple Support
If you see "apple.com/bill" on your billing statement
If you see "apple.com/bill" on your billing statement – Apple Support (UK)
If you see an unexpected charge
You can request a refund* for a purchase that you don't recognize, but you must pay for the purchase first. You can also cancel a subscription if you don't want to continue it.
*You must request the refund within the refund period.
Refunds are not guaranteed. For more information, see the Terms & Conditions.