iphone unlock question

oznature

i bought an optus iphone 4 from internet.
the seller also gave me the proof of purchase(original tax invoice and his name, phone number, date of birth).
now how can i unlock it? i try call to customer service but they said only the account holder can unlock it.
please tell me how can i unlock it,thanks

instsunshine

叫seller帮你解锁才行