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That is a SCAM message. Don't call that number. Follow the steps below to remove that message.
Close Safari by pressing the Home button.
Then without opening Safari, open Settings app, select Safari. Tap Clear History and Website data button. Press home button to close that screen. That should remove the scam message. You can now open Safari without getting that message.
If you have any questions or would like any additional information, please don't hesitate to ask.