One of my users cannot upgrade his account

One of my users was originally the business admin on our Voiceedge account, and wound up having to provide a secondary email address rather than his company email address when our account was moved to the new portal. He cannot use the Comcast Business app on his phone any more. It says 'business voiceedge account update required, to continue using this Comcast Business App please update your sign-in credentials'. When he tries the update now link and gives his company email address, it says user account already linked, but won't let him proceed further. 

I have tried adding his address as a new user on the ManageUsersSettings page. It tells me the email address selected is already registered, even though it does not appear on the list of users on the ManageUsersSettings page. The secondary address he gave appears there- and is not assigned to a phone number, it's just listed as 'unassigned' and 'primary manager'.

My user needs to be able to make outbound calls through the app and to log into his account properly.