In reply to a post by georgelnx:

As long as user xyz isn't connected then you will be able to connect. The Radius system (Plusnet Login Servers) will get confused when the real xyz tries to connect and reject them. Then the fun starts.

Not always, you may find, both are allowed to login and both get the same IP. In that case, both will likely see major routing issues and inaccessibility issues.

Matt

In reply to a post by ukhardy07:

The ISP also will not release details of what each firmware upgrade changes. The changes they make are effectively a black box, but are designed to ensure the service continues to function whilst you are with the ISP.

Precisely why I don't use an ISP issued router.

That raises the question of what password was the OP using on xyz. If the stored one belonging to xyz I agree. If his own, then the line authorisation theory is most likely.

Hence my suggestion of literally typing in the letter xyz in front of the @, and seeing whether or not it connects.