What do you have to gain by turning them in?
Why is this your issue?
I’m a big believer in doing the right thing, but this screams “vindictive” to me.
You know the old line: “You’ve got to clean up your own back yard before you start on the one next door.”
I would drop this immediately. But I would let them know that I’m planning to hang up the phone each and every time they brag about cheating the system. Then I would hang up.