My iPhone has been hacked what can I do?

No, it has not been hacked. The message is a very common scam attempt. Close the offending page and avoid sites that are involved in such bogus advertising tactics.

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

Phony "tech support" / "ransomware" popup… - Apple Community

Your iPhone has not been hacked. That is a scam to trick you into buying a useless app and probably a VPN service that will steal your data. Just delete it and ignore it. And don’t click “close”; it isn’t a close button at all, it will execute a JavaScript procedure that will mess up your browsing. Instead go to Settings/Safari and tap Clear History and Website Data.

That message if fake, you have not been hacked and don't click on anything in that link or buy anything for resolving hacking.