Computer just got hacked, what can I do?

How do you know the number was from apple? Never believe anything that pops up magically on your computer saying to call some number. Apple messages don't include a phone number.

Look on your product documentation for the number to applecare.

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Clear your internet browser cache to ensure no malicious data is in your browser. If you're using Safari, open Safari preferences, then choose Privacy. Click on Manage Website Data, then click Clear All.

Check if System Integrity Protection is enabled. It's an important protection for your Mac that prevents anyone from modifying critical system files. Even though hackers can't modify this protection without first restarting your Mac and booting the hidden Recovery partition, it's a good idea to make sure this protection is enabled. Open Terminal and execute csrutil status. If you see the text "System Integrity Protection status: enabled" and it doesn't say "Custom Configuration" then you're good to go.

If the hackers directed you to go to any sites or were able to remotely control your Mac, you may want to consider downloading Malwarebytes. It's a free antivirus application that will scan your Mac for any malware that could have been installed by the hackers. Download it here: Malwarebytes | Free Cyber Security & Anti-Malware Software

You may also want to check your Applications folder. Verify that there aren't any suspicious applications, and if there are, move them to the trash.

Hope this helps!

Avoid phishing emails, fake 'virus' alerts, phony support calls, and other scams - Apple Support