Error when signing in: “”it looks like someone else is using your account, and won’t let him sign in”

Hello, my son is experiencing a similar problem with hotmail. He recieved a message saying "it looks like someone else is using your account, and won't let him sign in. We've gone through all the links, completed the questionaire, and all we get back is an email saying we haven't provided enough info. We provided answers to all the questions we were able to, but NO SUPPORT! Who can we contact to have his account reset?