The page/pup-up you saw is a common scam regularly seen on the internet. Generally, it poses no problem as long as you do not call the number or interact with any links embedded in the page.
To be on the safe side, however, you can check your system to verify no adware/malware was maliciously installed.
To do so, download Malwarebytes Anti-Malware at the following link:
It removes all known adware from your Mac. It is very simple to use, and should clean up your system in less than a minute, from start to finish. Just install the app and run it, then click the Scan button, and remove anything that is detected. Done!
Additionally, you can also clear any cached website data in Safari;
Click "History" from the menu bar
Select “Clear History and Website Data...”
Click the "Clear" pop-up and choose "All History"
Then click "Clear History".