I NEVER answer. But they call me 3 times a day. I'm getting very impatient with it all! I tried calling back today but it doesn't let you. When they call again I'm letting someone have it.
That might make you feel better, but if you're able to do it, make sure the caller doesn't even get an automatic answer. Do NOT attempt to call the numbers back, either. If the number is working, callers may benefit more than you because you signal yours works along with risking a hearty price, or getting the wrong person. Dialing numbers that only ring bother them more than getting cussed out by receivers.
I get this several times a week. It's a "free government grant" scam. I finally installed an app called Hiya on my cell phone (only one I have) so they don't get through. They still try though.