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20 spam calls per day? That sounds like torture... is there really no body in USA that would prevent that from happening? (I've never received a spam call on my now 20 year old phone number.)
Unfortunately it doesn't work that way, the ones that DO give you the option to be 'do not call' will forward your number to other spammers, actually increasing the spam calls you get. Do not ask them to put you on the d-n-c list! Here's what does work (in my experience): answer the call, but say nothing, heck, mute your phone mic if you have to. Just give them silence. I'm not sure if there's some 'person on the oth…
I don't get that many spam calls, but what I do when I get one varies from answering and immediately hanging up to doing what you suggested (which usually results in them disconnecting after about 5 seconds). Occasionally, I've done things like answering the call and snapping my fingers in the receiver instead of saying "hello" and that usually results in an immediate disconnect.
I'm not sure if any of those things have affected the volume of spam calls I receive though.