Oh, you have reached the maximum device limit. That was missing from your original post and that makes a difference. 
You indicated you already submitted a wallet unlinking request. It can take several weeks for that to go through. If you are still getting the same message, you can direct message (DM) one of the moderators and ask for an update. They may or may not answer.
What mobile device do you have? If it is iOS, Brave Rewards are not supported because of Apple policies:
If you have a slot open and are using an Android device, make sure you are updated to the latest version of Brave and try these other actions that have solved previous errors:
If none of that works, you can send a direct message to the moderators and include the following information for your device:
- Copy/paste your Wallet ID (found on brave://rewards-internals )
- Your OS and Brave version (first three lines in brave://version )
- A screenshot of your Rewards panel in `Settings → Brave Rewards
Mattches and Steeven are the moderators who handle most of the rewards issues.
How to DM a moderator:
- Click on their icon and select the Message button in the top right corner or
- You can go to your profile and create a new message in Messages.