You could log into your Roku account at https://my.roku.com and remove your payment method, I guess. I believe that would also prevent any recurring payments you already have in place from being paid.
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