Communication through kids needs to stop

My 8yo came home yesterday with a message from mom: "Tell dad the tuition payment is due." Not a text. Not an email. Told through my child.

Then yesterday he said "Mommy says you're not sending snacks for the school week like you're supposed to." AGAIN, through him.

I get it, we're not friends, but using our kid as a messenger is making HIM anxious. He's starting to act like he's responsible for managing our communication. I need to figure out how to shut this down without escalating things.