Your account gets locked if you connect to WoW from different Internet connections.
For example, if you connect from a broadband connection and then from a dynamic 3G connection (on a laptop or to the Remote Chat app for smartphones), your account gets locked and you need to reset your Battle.net password.
There is nothing to do except resetting the password.
Not even those from Blizzard can whitelist all your internet connections if they are dynamic.
To reset your password, follow the link from the error given when you try to log into World of Warcraft.
You will receive a verification code by SMS to the attached phone number from your Battle.net account.
If you don’t receive any code, you can call Blizzard support by Skype at this number: 0800 0288246 (you need to choose the UK flag from Skype, before calling).
The call is free, you don’t need to have any Skype credit.
If these methods don’t work, just go to the World of Warcraft website, look for the support section and submit a ticket.
Most likely the support admins will fix your issue.