@Rounak ck,Thanks for posting in Q&A.
From your description, I know you got an error when your open company portal.
Based on my research, the error message means the device is already enrolled in another organization's management.
Here are some solutions you can refer.
1.Check for Existing Enrollment: Go to Settings > Accounts > Access Work or School on the device. If there are any work or school accounts listed there, it means the device is already enrolled. You might need to delete these accounts.
2.Registry Keys: If the device was previously enrolled with another management system, there might be lingering registry keys that need to be cleaned up. Look for GUIDs under HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Enrollments and delete them, ensuring not to delete Context, Ownership, Status, and ValidNodePaths.
3.Reset the Device: If the device is not enrolled in another MDM, you can try resetting the device and then enrolling it in Intune again. To reset the device, go to Settings > Update & Security > Recovery > Reset this PC.
4.Change automatic enrollment status. Go to Intune portal > click devices > click Enrollment > click Automatic Enrollment > change MAM from All to None, MDM None to All, unmanaging the devices currently in AAD, then then adding them again via the Company Portal.
Please try above information, if there is any update, feel free to let me know.
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.