How do I resign up?

I am (or was a box user) as an individual contractor working with a Federal team. I was told that a "migration" was occurring on 17 September and that I would have to re-sign up for the Box tool and then have my Fed partners re-invite me to our collaborative documents.  I was shut out of the documents and my connection on the 17th and as I went to sign up for Box as directed, it won't let me use the e-mail I had previously used. That e-mail is in fact the e-mail that I use for work. I want to reuse it, as my working business partners use that in regular/all communications. How can I sign back up in Box using my e-mail (without changing) so I can have business partners re-invite me to joint work/records?