I have subscription-based Channels in one or multiple TV Apps, but the Apps are advertised as “Free” by the different app stores. Shouldn’t they be advertised as “Paid” apps?

They shouldn’t because the download of the app is free. It is important that it is free, because you would otherwise be losing potential customers. The App Store might, at its own discretion, promote it as a “Free” App, because the Store does not charge a fee for the download and installation of the app and because some of your integrated Channels/Categories may be indeed free, while you charge only for “Premium” content in selected Channels/Categories within your app.