Hi @nex2, sorry to hear about this.
From your description it sounds as the theft protection called My Xperia Theft Protection has been activated. To unlock Lockdown by my Xperia you have to log in using the same Google account which you used to activate the service in your device. Unfortunately there is no way around this due to security reasons.
If you do not remember your Google password you may reset it using the following link https://www.google.com/accounts/recovery/. Keep in mind that it will take 24 hours after the reset before you can use the new password to authenticate yourself on the phone.
If you still are unable to log in after this I can only advice you to have your device sent in to an authorized service center in order to have it unlocked. In that case I suggest that you get in contact with your local support team for instructions on how to send the phone in.
