@Laura18-
When the channel is one for which you have a paid subscription through Roku, there will be a "Manage subscription" option instead of a "Remove channel" option. You can click this and follow the prompts to prevent any more payments, but your subscription and channel access will continue until your subscription period runs out. Due to a programming decision by Roku, you will not be able to remove the channel app via the Roku interface until the subscription period runs out.
Instead, try removing the channel via the official Roku remote app on an Android/iOS phone/tablet connected to one of the Rokus on your account. At the bottom of the first screen, click Search and do a search for the installed channel name. On the resulting screen you should get options to Launch the channel on your Roku, or Remove the channel. I've never tried to remove a subscribed-thru-Roku channel (I haven't had one for years, and this may give you an idea of one reason why) but others have reported this works with active subscriptions through Roku.
Roku Community Streaming Expert
I am not a Roku employee, only a user like you. Please, no support questions via private message -- post them publicly to the Community where others may benefit as well.
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Ultra 4800 | Streaming Stick 4K+ 3821 | TCL Roku TV 43S245/C107X