How to unlock a locked Iphone 5?

I received an iphone 5 today that I ordered from ebay. The ad for the phone said UNLOCKED Apple iphone 5- 16 gb -Black and slate smartphone. I read the reviews and feedback about the seller, and he seemed rather reliable. Today when I received the phone, I plugged it in to the incredible disappointment of the phone having a pass code. I messaged the seller, he responded with a pass code and asked me to reset the phone, because obviously it didn't reset. The passcode he gave me was incorrect, and I can't reset the Iphone from iTunes because the only way to allow access of my computer, is to respond from the phone, which I can't get into. I don't have his apple ID, and I don't know how else to get into the phone. I've looked up hacks to get into the phone, but they all require making an emergency call, then canceling it, but I can't even do that because the phone doesn't have any service, and will not make a call. Can anyone help me?

Demand to return the phone for a full refund. If the seller refuses open a case for item not as described.