The Joys Of Telephones

I just got a call from a computer voice telling me that the call is from the IRS and that they are about to file suit against me.  Then the computer voice tells me that I can arrange a settlement if I call a particular number.  Yesterday, I got four calls from the "warranty department" offering me a "final chance" to extend my warranty on a car that I have not owned since 2012.  Despite telling the caller that I had no such car, the calls continued.  Early this morning, I also got a call from a computer voice named "Bridgette from Cardholder Services" who gave me the chance to save huge amounts on my credit card bills.  On Monday, I got the call in which a recording tells me about the huge rise in crime in my neighborhood and then offers me a chance to get a security system at a discount.  The only one of the standard annoying calls that I have yet to get this week is the one from a heavily accented person who tells me in hard-to-understand English that he or she is calling from Windows because my computer keeps sending them error messages.

Why is it that these scam calls just keep coming?  These annoying attempts to swindle me are in addition to the many fund raising calls that I answer each week.  I put my number on the Do Not Call Registry, but it had no effect.  I've tried telling people nicely not to call because they are wasting their time.  After all, I already know that these calls are scams.  That too had no effect.  I've tried yelling at the callers, but they just hang up.  Still, I come back to the original question:  why do they keep calling if they already should know that they will not trick me into their scam?  It certainly is a mystery to me, a very annoying mystery.