Have you gone to https://my.roku.com logged in and gone to the Manage your subscriptions page? If not, do that. Was there anything there?
If so, you may want to add a PIN to your account from the PIN Preference page. Oh, and then unsubscribe.
If not, then Roku didn't bill you, at least, not through that Roku account. If you have another Roku account, check that one too.
Roku Community Streaming Expert
Note: I am not a Roku employee.
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