A few accounts simply don't seem to be migrating to the new platform properly, you can usually still access them using the IP address of the old POP server. You may find it helps to refresh your account by going to
http://autoreg.autoregister.net/cgi-bin/chgpwd and entering your username and your current password three times. I've not seen much success with this but it doesn't hurt and may prevent you having to call.