Is this a scam?

Two men have just knocked on my door claiming to be subcontracted by Virgin Media saying that they had detected interference coming from our router. They were in an unmarked van, wearing orange hi-vis vests with Virgin Media on the back. The first man had a broken ID badge that was just a red card with his name and photo on, no Virgin Media branding. They said they needed access to the property to look at the router. I said I felt uncomfortable about it as I hadn't been contacted beforehand. I asked to check and if they would be around in the area and could come back later. They said yes but that if they kept being denied access then Virgin would put a block on our broadband. It all seemed quite suspicious so I didn't let them in and they were fine about it then drove off quite quickly.