Hi and thanks for your question.
Can you tell me the exact version of OS X you are currently running, please?
Click the Apple logo in the menu bar at the top left of the screen
Select "About This Mac"
In the window that opens, look for the "Version" information. Please let me know what it says.
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".
You are very welcome!
When the current question has been answered to your satisfaction, please remember to rate me accordingly when you get a moment. Otherwise, feel free to ask for additional help with this.
Please feel free to request me again when you come back to ask another question. Insert “For John T. F. only” in your initial question and you can, also, submit new questions directly via the following page:
In the Safari menu bar at the top of the screen, choose "Safari"
then click Preferences
Next click Privacy
Look for a section labeled "Cookies and website data" and choose one of the options. The default is "Allow from websites I visit".
Great! Glad to hear it.