Issue with creating mobile users

We created about 190 mobile users for training purposes on a CommCare Pro plan. After completing the training, we deleted all users to enable us start from a clean slate. Before deleting the user names, we downloaded user info in Excel for bulk upload. However, CommCare is not letting use the deleted user names and gives this error message: “Username xxx belonged to a user that was deleted. Reusing it may have unexpected consequences.” We must use the deleted user names for various reasons. We would appreciate your thoughts on how we can resolve this issue.