If you wish to keep using Roku features you can purchase a Roku device and set it up on your Samsung, linking the Roku to your current Roku account.
If not, your Roku account does not know you no longer have a working Roku TV, so your subscription fees for anything you have subscribed to through Roku will continue to go on charging you. To prevent this, log into your Roku account at https://my.roku.com, scroll down to "Manage your subscriptions" and cancel any subcsriptions shown there. I would not cancel the account itself until you have confirmed that your subscription fees have stopped. Meanwhile if you are no longer using the RCA Roku TV, you can unlink it from your account, under "My linked devices".
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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Streaming Stick 4K+ 3821 | Streaming Stick+ 3810 | TCL Roku TV 43S245/C107X