Obvious scam since the scammers always display prices like $299, $399, etc. for their "services", which are outlandish prices that no one would ever pay.
Microsoft provides Windows Security with Windows Defender AV in Windows 10 for free, so why pay for anything else?
If a telephone number was displayed on a web page or worse yet, the scammers called you directly, they're even more obviously fake, because no valid professional business would ever do this.
There are reputable pages from both Microsoft and others all over the net with pages and pages of text and pictures explaining this, including pictures of many of the same web page popups or lists of phone numbers or scam scripts used in fake tech support phone scams, but all of them really come down to the simple sentences above.
No one calling or popping up advertisements (that's what they are, since valid alerts never include phone numbers) on your screen is ever worth contacting or talking to. Just hang up or figure out (ask here) how to close the popup and get on with life. It's a fake.
Rob