Spray the inside of the slow cooker with non-stick cooking spray.
In a large bowl, whisk together the melted butter and flour until smooth to create a roux.
Gradually whisk in the whole milk and heavy cream until fully combined and smooth.
Add the garlic powder, onion powder, salt, black pepper, and smoked paprika to the milk mixture and stir well.
Add the uncooked elbow macaroni to the slow cooker.
Pour the milk and butter mixture over the macaroni, stirring gently to combine.
Cover the slow cooker and cook on low for 2 hours, stirring once halfway through cooking.
After 2 hours, add the shredded cooked chicken, shredded cheddar cheese, and shredded mozzarella cheese to the slow cooker.
Stir gently to combine all ingredients evenly.
Cover and cook on low for an additional 1 hour, or until the macaroni is tender and the cheese is melted and creamy.
Stir the mac and cheese before serving to ensure even creaminess.