Adding to what @RokuDanny-R said, are you currently paying at all?
Roku itself doesn't have any fee. (ie: you just buy it, hook it up and it gives you thousands of channels - many or most of which are free/advertiser supported.)
You can add premium channels and there are often more than one way to pay for them. For example you can subscribe to them directly and then log into them on your Roku. Or you can subscribe to them via the Roku, and then you will get a charge like: Roku for [name of service].
Most channels have multiple ways to subscribe, and the subscriptions are typically unaware of each other.
For example, if you have a Hulu account, then bring up the Hulu channel on a device like a Roku, then sign up for an account rather than sign in with your existing account, then you'll have two. In that case, pick one and cancel.