So here is a New York Times article on the subject. There are a few good ideas, but another layer is to always block your caller id and only unblock it for contacts you trust. Here is the FULL ARTICLE, but I summarize below

Rule No. 1 The most simple and effective remedy is to not answer numbers you don’t know, Mr. Quilici said.

“Just interacting with these calls is just generally a mistake,” he said.

If you do answer, don’t respond to the invitation to press a number to opt out. That will merely verify that yours is a working number and make you a target for more calls, experts said.

List your phones on the National Do Not Call Registry and report them there!

Use apps such as Truecaller, RoboKiller (fee), Mr. Number (owned by Hiya<below>), Nomorobo (free for landlines, fee for mobile) and Hiya (fee??), which will block the calls.  (Note: I have not reviewed any of these for security issues, so caveat emptor)

Phone companies, such as T-Mobile, Verizon and AT&T, also have tools to combat robocalls. They work by blocking calls from numbers known to be problematic  (Note: Oh yea, after being going through 10 minutes of voice response and being on hold for another 20 minutes)

Turn the tables And then there is the Jolly Roger Telephone Company, which turns the tables on telemarketers. This program allows a customer to put the phone on mute and patch telemarketing calls to a robot, which understands speech patterns and inflections and works to keep the caller engaged.  (Note – I kind of like this idea, but many of these miscreants use fake caller IDs of legitimate business phone numbers. Also note, the services is NOT free, but not that expensive either for that matter.)