Notification of being hacked on iPhone

This is a scam message that is trying to trick you into providing your personal credit card information to buy completely useless software to fix a problem that your phone does not have.

Ignore the message and delete it. Do the same with other similar messages that you will surely see again.

Your phone has not been hacked, it is a scam message designed to get you to purchase unnecessary software or phish for personal information.

Read more about it here -

Recognize and avoid social engineering schemes including phishing messages, phony support calls, and other scams - Apple Support

It's a scam. You are not being "hacked".