The problem with your method is that spammers call phones just to see if they pick up. This then confirms an active number that they maintain in their lists. This can be done legally because technically calling and hanging up and never calling again (from the same number) isn't spam. So just don't answer.
Not the ones from politicians.
I presume this is because these spammers just keep selling other spammers valid phone numbers to add to their own lists.
The only phone number that gets spam calls anymore is that Google Voice number.
For all other numbers, the calls have virtually stopped.