How to turn off iphone 5c lost mode?

Okay so i just bought a iphone and the guy i bought it from for some strang reason trying to be funny by turn my iphone on lost mode i called the dude but he's not answering his phone and now i'm stuck with a iphone that i can't use so is there any way i can turn this stupid thing off

Sorry. It's probably stolen. It also is probably being tracked.