I subscribe Discovery plus through Amazon. Why am I being charged through Roku just because I watch it on my Roku tv?
Log into your Roku user account (https://my.roku.com). You can see any subscriptions you have with Roku there. See if it's listed there, and confirm you also have it through Amazon. Then remove one of the subscriptions.
When you subscribe to a premium service like Discovery Plus through a third party (Roku, Amazon, Google, Hulu, etc.) you typically can only view that premium service through that third party.
If you've added Amazon's Prime Video to your Roku, can you access Discovery Plus through your Roku Prime Video channel app?