Safari has locked due to "illegal activity"

iOS

Scam popups, phishing attempts, “virus”alerts, etc

1. Force Close Safari. https://support.apple.com/en-us/HT201330

2. Clear history and website data from Safari: https://support.apple.com/en-us/HT201265

3. Stop pop-up ads on Safari

"Pop-ups and ads in Safari

If you see an annoying pop-up in Safari, you can go to the Search field

and enter a new URL or search term to browse to a new site.

If you don’t see the Search field on your iPhone, iPad, or iPod touch,

tap the top of the screen to make it appear.

Some popups and ads have fake buttons that resemble the close button, so use caution if you try to close

a pop-up or ad. If you're unsure, avoid interacting with the popup or ad and close the Safari window or tab."

Section: Close pop-up ads on your iPhone, iPad, or iPod touch https://support.apple.com/en-us/HT203987

4. Avoid scams: https://support.apple.com/en-us/HT204759

This is probably because your browser has been hijacked by malware. Download Malwarebytes (the free trial edition) and run a scan. Also, go to Safari>Preferences>Extensions and remove ALL extensions that are not by companies that you recognize and remember having downloaded the extension from.