NO ONE from MICROSOFT will ever call you or POP UP on your computer screen with a legitimate problem and phone number to call. These are very good scammers. If it is a phone call, hang up, no need to be polite. If it is a pop up, CLOSE your internet browser (Internet Explorer, Firefox, Chrome), but if you cannot close the browser the normal way, shut off the computer. The pop up should disappear from your browser when you turn the computer back on and go onto the internet.
The scammers are excellent at what they do. They may have your computer make noises at you, or put pop ups on the screen that claim you have hundreds of viruses, etc. ALL FAKE NEWS. And they make it near impossible to remove the screen unless you shutdown your computer. Go ahead, shutdown, you won't cause any harm, even if you have to hold down the power button for 10-15 seconds to get the computer to shutdown.
You wouldn't invite a stranger into your home, would you, if they knocked on the door and told you that your house had a problem? (Please tell me you wouldn't, your protective radar would be in full force, right?)
DON'T invite anyone into your computer that CONTACTS you. It's a different scenario if you have initiated the technical support phone call. Then, they may ask if they can remotely look at your computer to diagnose and potentially fix your issues. At that point, you may allow the connection because YOU made the phone call, and hopefully... you called a legitimate technical support number. Be aware of numbers that are associated with "Microsoft certified technicians" (substitute other company names here for Microsoft). THIS IS NOT MICROSOFT, and they hope you didn't read their description closely so that you would contact them, thinking it was Microsoft.
ALWAYS REMEMBER: before calling for help - is it plugged in, and is it turned on?