It's not a scam.
Last week I got from a man claiming to be from Virgin calling because my broadband was reporting as being slow and he had been told to fix it. He didn't know my name, account number or anything - he insisted he had been contacted by Virgin.
He didn't ask for any name or password but he did want me to log in to a website that would have given him remote control of my computer. I told him to bog off - that was definitely a scam, the same one as callers purporting to be from Microsoft.