Hey there. To clarify, you can change your channel name up-to 3 times in 90 days. If you've changed it recently, you might have to wait a bit longer. Here's more info: https://yt.be/help/znjF . Let us know if this isn't the case and we'll look into it.
To help the right team better investigate, please send a feedback report from your account with these steps: https://yt.be/help/feedback . You may not receive a response, but the details will help us identify and fix issues. Thanks.