Well done for being suspicious, many people are caught by this type os scam
Microsoft will never, ever, cold call a customer, this is a well known Tech Support Scam.
If ever someone claims to be from Microsoft in a webpage, or provides a phone number on a web page, or cold calls you, it is always a scam, Microsoft could not possibly know if your PC was infected (it is not), these scammers just prey on people to try to scare people into thinking there is something wrong with their PC