I know that just answering and hanging up is enough for the Robo callers to know yours is a live number. So the best action is to let it ring. I can turn my phone over and the ringing sound stops, the caller still gets a ring tone. It will go to voice mail eventually, but usually the robo has hung up by then. Anyone leaving a message about IRS actions gets reported to the FCC and the number get blocked.
This is the link for the FCC - this forum converted the url to a nice looking Ad...
Do you receive unwanted calls or texts from telemarketers? Is your own telephone number being spoofed, blocked, or labeled as a possible spam call? The FCC is committed to doing what we can to pr...
consumercomplaints.fcc.gov
You should have the ability to block numbers, calls and text. I long press a phone number and can choose Block on my phone. For Texts I have to manually type the number in the Block number setting.
Look in Settings/ Call or Phone management, perhaps... you should see something like call blocking and decline with message if you are using an Android phone. Also look at the Answer calls setting. Turn off Auto answer, this way you aren't answering the phone by picking it up.
I added a special ring tone for just my contacts, and left the default ring tone for unknown callers, that way I could decide to answer or not.
The service providers aren't going to do much, mostly because there isn't a lot they can do either. My provider blocks known 'bad numbers' but these people just rotate through numbers, so keeping the list up to date is hard.