If you want someone to stop being dishonest, it’s better to appeal to their sense of nobility than to do anything that would make it difficult for them to save face.
“I’m disappointed” is better than “You’re a liar”.
Condemnation doesn’t provide them with an out. In their mind you’ve already made your decision about them. So they’ll be defensive. And they’ll be angry with you for being judgmental.
You don’t want them to think you’re angry. You want them to know you’re hurt and that you know they’re better than the way they’ve been behaving.