It sounds like a scammer has control of your Roku device and put it into Guest Mode and added that message. IT IS A SCAM! I'm not sure how to get it out of Guest Mode, but the first thing to try is a factory reset.
How to factory reset your Roku® streaming device | Official Roku Support
Roku Community Streaming Expert
Help others find this answer and click "Accept as Solution."
If you appreciate my answer, maybe give me a Kudo.
I am not a Roku employee.
