Only one option then factory restore it.
By doing this it deletes all your contacts ect.
So if you were wise enough you should of used a cable and backed the contact list up to a Pc.
Or created a backup of it on your memory card.
As a hint look on google for Galaxy s2 factory restore mode.
It will tell you there, You can understand why it wipes all the data because it is a security measure if the phone is stolen. Or you lock yourself out of the phone.