http://unlockbootloader.sonymobile.com/instructions
Si no puedes pasar del segundo paso tienes que pagar si o si para abrirlo.
In your device, tap
Service info > Configuration > Rooting Status. If
Bootloader unlock allowed says
Yes, then you can continue with the next step. If it says
No, or if the status is missing, your device cannot be unlocked.
Un saludo