It's always a good idea to actually post content, and not rely on just a title. That's true all across the Internet.
Be aware that subscribing to Fubo TV directly means you can use the credentials on any device, including Roku.
Also be aware that subscribing to Fubo TV (or anything, really) via Roku Pay, usually limits your viewing to Roku only. With very few and very rare exceptions, don't have to subscribe through Roku to watch something on Roku.
And, be aware that a subscription to directly to a service (such as Fubo TV) is a totally separate subscription from a subscription through Roku Pay.
My guess is that you subscribed both ways, and are being charged each way. Remember, they are totally separate subscriptions.
I would suggest you decide which you want (hint: direct subscription to Fubo) and notify the other that you subscribed in error, thinking it was a glitch in the system, not realizing you were being charged twice.