Re the serial number part of your post:
Over the years Roku sometimes has been inconsistent in what they are calling serial numbers and what they are calling device numbers.
Try logging into your account at my.roku.com and scrolling down to the list of your linked devices. You may get a different serial number to try there.
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