Thanks for the info here. You'd be seeing two authorization charges because subscribing to the Starz service directly through 'The Roku Channel' is an individual service, and subscribing to Starz directly (outside the Roku channel) would be a different service entirely. If you subscribe to Starz within The Roku Channel, you'd need to watch Starz inside the The Roku Channel, and not using a separate channel (app).
When you tried loading The Roku Channel online, were you signed into your Roku account in the browser? Did you try clearing your browser's cookies/cache/history and then signing in once more? Did you also try loading the site in another browser (Safari or Firefox) to see if that cleared up the issue? You can see more about the browser requirements for viewing The Roku Channel on the web here: https://support.roku.com/article/360007223934-how-do-i-get-the-roku-channel-
Please feel free to PM me with your Roku account email address and more details if you need additional help, or still aren't able to watch The Roku Channel on the web after troubleshooting.
Roku Community Manager