When you say you are being billed for the subscription, how are you being billed and what does it say? We would first recommend logging into your Roku account online at my.roku.com and clicking Manage your subscriptions to see a list of current subscriptions that you are being charged for. If you do not see the subscription there, then you are most likely not being charged by Roku.
As @slstarks123 mentioned, more often than not, customers have accidentally created another Roku account and subscribed to a channel on that account and are being charged through there. Is it possible that you may have done this?