"Did it connect with the xyz username? "
Yes, that's the odd thing.
That was me, not BatBoy
What if you literally try the letters email@example.com?
I'm wondering two alternative things.
1) It was originally set up by person xyz who decided he didn't like it and reverted to his previous router. This has been known. Unlikely in this case, but possible.
2) The same piece of kit (badged as a Home Hub ver 5A) when used on BT needs only a dummy username and any or no password. This isn't inherently because of the router, but because the BT Consumer system picks up on the line number I believe. I wonder if you are on their new network and that works the same way, but they are keeping/publishing old-style usernames to keep it simple for support staff until everyone is on the new one.
Kindness isn't going to cure the world of all its awfulness but it's a good place to begin. Daisy Ridley.
My broadband basic info/help site - www.robertos.me.uk.
Domains, site and mail hosting - Tsohost
Connection - AAISP Home::1 80/20. Sync 59500/14989kbps @ 600m. - BQM