That's exactly what the stbx would do. That and start angrily blaming me whenever anything upsetting happened to him.
You can't add anything new to the discussion otherwise they'll twist it and throw it back in your face. Basically you just stick to repeating their lines - usually they'll have go-to phrases that they use over and over. Try to use those on them before they can use them on you. It shuts them down cold.
Be warned though, it is utterly emotionally exhausting. You can't let them see that you're any way affected by the hurtful things they're saying. You're reflecting them, giving themselves back to them, essentially closing the loop and refusing to give them the feedback they crave.