How to unlock a stolen iphone?

Okay so i bought an iphone on craigslist and when i went to the persons house to go buy it, it looked fine. And then i got home and tried setting it up but it says that the iphone was lost and if found to call that number. So i did and asked if they wanted 75$ back for it? They said no that they had already purchased a new one. So is there a way to get through to it?
(No dumb comments please -.-)

You'll have to call them back and pay them $75. Why? Because their iCloud activation lock is on it. Without them removing that phone from their profile and logging out of that phone, you will not be able to activate it. Also, ask them what network it was on. That owner will also have to contact the carrier to have it unlocked for you to use on another network. Apple or their carrier will not speak to you. They don't get involved in the drama of third party transactions and honestly they don't care. So make a deal to pay half up-front, the other half when it's done and confirmed. Trust me, it'll be cheaper than doing it any other way and be glad the person actually answered your call. That rarely happens. Right now it's just a pretty paperweight. Many good deal iPhones on Craigslist are lost/stolen so this comes as no surprise. Best luck.

You would have to ask the original to contact the service provider that blocked the phone to get it unblocked.

You can't as its a security feature (which is a great feature). The person that had it originally will need to wipe it before you can set it up as your own (which means they also know where their phone is at on the map since they can track it with find my iphone).