Wrong name and e-mail associated – can't invite to Sharepoint website

Hello,

My company has a "invites only" website for partners setup in Sharepoint. I am admin but have a problem when I try to invite a specific person. There is some kind of mismatch. Whenever I try to type this persons name or e-mail into the invite feature someone else's e-mail is put there instead. Example:

If I type Sam Smith or sam.smithATSIGNcompany.com it is always replaced with John Doe and john.doeATSIGNcompany.com. Why is that? Where can I change the association?

Kind regards,

Jesper