I have the same problem when move my website.
I own the free sub-domain named "bluezone.netau.net" with Account email@example.com before. And I try to move it to new panel today.
I had already delete old account in the old panel.
Then I try to create new account, howevery , the sign up tip me that "Please use an email address from a reputable email provider (like GMail or Yahoo)." It seems that I cannot use the old email to sign up new website.
Then as a result, I have to use my Gmail to register it.
But I hope to get back the old free sub-domain named "bluezone.netau.net". However, I got the message about "subdomain is already taken".
But I had already delete old account in the old panel, so I cannot login again...
Please help me to get back it, thanks so much.
I remember my password for old panel , Or I can send an email by firstname.lastname@example.org to prove I am the owner of this old website.