877-852-3896

Computer scam . popup window opens up claiming your mac computer has a virus. Posing as Apple care.

Scam message

I received a pop up message with Apple Care logo, warning me to call 877 852 3896.
The message said my laptop was infected by a serious virus and 2 malicious malware.
The message warned me to not use my computer until i called that number.
Like the Fool-I-Am, I called.
A man with a South Asian accent answered (I lived in India & Asia for years & recognize the accent).
He was polite & plausible
He warned me to turn off my laptop immediately & not to use it..
He Asked if I could wait for his "technical assistant to call me back within 90 minutes".
I said yes, I gave him my cell number, foolishly..
That was 45 minutes ago & They have yet to call.

What do you advise?
Can I use My laptop now?  I still haven't turned it back on.
SHOULD I ANSWER THEIR CALL BACK?  OR HANG UP WHEN I REALIZE ITS THEM?

This “error message” suddenly appeared on my iMac Pro and I cannot delete it.  The phone number, according to Bing, is a scam.

Same issues as RB above, but I hung up after the statement that I should wait 90 minutes.