Unable to remove user from workspace (group)

We are having hard times removing a user from our workspace (group). On the Edit Group option, we click the trash bin icon for the user and click save. The dialog closes, but after opening the Edit Group option again, the user is still there. After refreshing the page, the user is still there. After few days have passed, the user is still there.

See image. The user in question is in third row:

https://www.dropbox.com/s/t5i5cjr1mew1flk/Capture.JPG?dl=0

As you can see from the image, we are not able to give that user a role. I think he had issues merging his previous Microsoft account with Power BI account. Anyways, we don't want to see that user on the user list anymore.

Thanks!