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That is a SCAM message. Don't call anyone. I hope you didn't Safari from Applications folder.
Press Command, Option and Esc keys and this will bring Force Quit window. Select Safari and click Force Quit. This will close Safari. Ignore this step if Safari is already closed.
Go to Applications folder. Then hold down Shift key on your keyboard and open Safari. Click on Safari menu and select Clear History and Websiate Data. On the dropdown next to Clear, select All History and click Clear History. If you see Reset Safari, then click Reset Safari and reset it.
Then click on Safari menu and select Preferences. Then click on Privacy tab. Click Remove All Website Data. Click Remove Now. Restart Safari.
Please let me know if that didn't work, so we can continue troubleshooting.