from memory you can only change it from within CPANEL. Are you going to cpanel via your hosts own web interface? Perhaps try that. If not, then you might need to contact them. good luck!
Ask your host via support ticket? (If it shared or managed server)
Check your email? (Maybe they are sending some kind of activation email)
Try to login into your cpanel or WHM with root account and password?
Just be sure the email addresses on each of your cpanel accounts, is secure/valid.
If someone hijacks your email and it's linked to a cpanel account, they can gain access to that cpanel account with a password reset. (obviously hehe)