SCAMS.
In agreement with the previous posts but I have changed my position on "wasting their time". Did that for quite awhile as time, mood, and circumstances permitted.
Does not stop them and only flags your number as being "live". They sell your number over and over and you will get more and more calls.
I had gone to the extent of looking up and printing out the website screens of the sites they wanted me to go and download stuff. Usually some software that would give them access to and control of my system.
When they called I unplugged my network connection but could pretend I was connected (by describing where I was "on the screen") as they told me to do. Claimed Error 404. Typed letters "D" 'O", "T", instead of a period. Claimed I could not hear them due to the background noise and/or accents.
Drove them nuts but overall but they then kept trying and trying.
I got Nomorobo and pretty much ended the matter with such calls especially Windows Services and Credit Card Services. However the latter has just lately been able to get back through and are again leaving answering machine messages.
Reedo_43's advice "Just hang up" is the best way to deal with them.
(And by the way the IRS will never call you either. Those fake calls will start next and show a government IRS number, the caller will have a badge number. They will threaten you with jail, "the police are on their way", they will know and tell you the nearest location to immediately wire them money. Do not do it. It is a scam. Hang up immediately.)