Keeping your account secure is your responsibility, but you should be able to recover the account by calling Playstation Customer Support at 800-345-SONY. Sony doesn't do this by e-mail, and it doesn't provide any support in the forums. You have to call on the phone. You will have to prove that the account is yours. You can do that most easily by telling them the date-of-birth, and security question answer, that was registered with the account. The person that stole the account can't access that information, so you are the only one that should know it. Once Playstation Customer support is satisfied that you are the legitimate owner of the account, they will change the sign-in e-mail and password to something that you can access.