@Samuel Santos, Thanks for posting in Q&A. From your description, I know the device will enroll again after the device is deleted in Intune portal.
Firstly, please check the device record in Intune portal to see if the "enrolled by" is the previous user account. If yes, it seems the user account is still active after the user leave the company. You can consider unassign Intune license from this user or disable/delete this suer account.
After that, delete or retire the device in Intune portal if this is a personal device. If this is a corporate device, you can also consider wiping the device for resetting a device before you give the device to a new user,
https://video2.skills-academy.com/en-us/mem/intune/remote-actions/devices-wipe#wipe
Hope the above information can help.
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.