I discovered why my Azure free trial was eating cash. It seems that the free trial defaults to reasonable paid service tiers, and not the free development tiers. So when you set up your Microsoft account (MSA) for development purposes, make sure you double and tripple check that the plan you pick starts with an F (for free) and not an S.
When you use bot builder or QnA builder, you might need to go back after you create a project from template and change the "App Service Plan" to something free. If you see your $ decreasing and you're not doing anything - you've configured something incorrectly.