I can confirm answering calls and using as much of their time as possible totally works. I’ve been doing this for a year or more now; I get excited when a spammer calls me now. It’s about a monthly affair.

I have a bookmark for https://www.getcreditcardnumbers.com/ - I happily give them all the credit card numbers they want (the ones from that site pass the checksum, but of course isn’t valid in combination with a made up expiry and CVC).

After a couple card numbers fail, they cuss me out, sometimes threaten my life, and never call again.

My theory is they get flagged by their payment processor if they submit many bogus credit card numbers.

It’s about a 10-minute investment once a month. Less time than I used to spend answering and hanging up on spam calls.