It is a common scam.
Tech Support Scamming through unsolicited phone calls, browser pop-ups and emails from "so-called Support Techs" advising "your computer is infected with malware", all your files are encrypted" and other fake messages has become an increasing common scam tactic over the past several years. The scams may involve web pages with screenshots of fake Microsoft (Windows) Support messages, fake reports of suspicious activity, fake warnings of malware found on your computer, fake ransomware and fake BSODs all of which include a tech support phone number to call in order to fix the problem. If you call the phone number (or they called you), scammers will talk their victims into allowing them remote control access of the computer so they can install a Remote Access Trojan in order to steal passwords and other sensitive personal information which could then be used to access bank accounts or steal a person's identity.
These are a few examples.
The scammer may claim to be affiliated with Microsoft or Windows Support. However, there have been reports of scammers claiming to be affiliated with major computer manufacturers such as Hewlett Packard, Lenovo and Dell, familiar security vendors like Symantec, Panda, McAfee, etc. and even popular ISPs. Microsoft does not contact users via web page messages, phone or email and instruct them to call tech support to fix your computer.
For more information about how these scams work and resources to protect yourself, please read Beware of Phony Emails & Tech Support Scams...there are suggestions near the bottom for dealing with scams and a list of security scanning tools to use in case the usual methods do not resolve the problem or you allowed remote access into your computer.
If you need individual assistance with a malware infection, you should start a new topic in the Am I infected? What do I do? forum.
OR follow the instructions in the Malware Removal and Log Section Preparation Guide. When you have done that, start a new topic and post your logs in the Virus, Trojan, Spyware, and Malware Removal Logs forum, NOT here, for assistance by the Malware Response Team.