Payment problem

iTunes charged me 20$ for something I didn’t subscribed.

Luckily I didn’t have money on my card.

Sure you have received an invoice from Apple, so read the invoice.

Tap on Report a problem on the invoice.

You need to cancel the subscription, see the following Apple articles:

If you want to cancel a subscription from Apple

If you want to cancel a subscription from Apple - Apple Support

If the subscription that you want to cancel is not listed

If the subscription that you want to cancel is not listed – Apple Support (UK)