Feel better after your rant? Now learn that the number on your caller ID was probably spoofed: Untraceable; originating probably in India or Pakistan, out of the range of any DNC list or AG or anything even remotely connected to US laws or regulations. Good luck trying to sue the pants or anything off them.
Oh and now that you called them back, they know your number is live and there is someone on the other end (you) who will engage with them. You will probably get many more calls from many other numbers. And don't overlook the vengeance callbacks you might get just because you were so eager to let them know how you feel.
You could do as I do - play dumb, waste their time getting them to "explain" - i.e, sell you on something you ain't buying. After 15 minutes, tell them that you're not sure they aren't wasting their time trying to explain, and you won't feel bad if they move on to another customer. If they press on, let them; you might be protecting some gullible fool from their scam. I kept a guy from India on the line for an hour an fifteen minutes while he was trying to get me to log into his website to "repair" errors in windows - he didn't know which version of windows i was running, even though he claimed that he could see my system & the problems it was causing on the net. (Mac OSX and windows 8.1 dual boot BTW; that threw him for a loop) When I pointed out that all those "system errors" he was going to "fix" for me on windows 8 were actually caused by Itunes trying to log me in to the Apple store where I don't have an account, and that I probably had forgotten more about the details of various OSes than he would ever know, and that he had wasted an hour of his life, but if he wanted to do it again sometime, please don't put me on their do not call list, he finally lost it. He started making rude anatomically impossible suggestions about what he wished i would do, and what he would like to do to me (I got nothin' against gays, but this guy - sheesh). When he was really wound up, I hung up on him. Haven't heard from them again, and I hope he broke his headset, keyboard, or monitor.