Congratulations you have won an iPhone pop-up

Every time I try to use safari on my iPhone 6 I get a pop up message saying "Congratulations! You won an iPhone press any button to confirm". It looks like the message comes from Facebook but obviously it's not. The first time it comes up you can select cancel and it goes away. The second time there is no option other than to press ok or close safari. I cannot use the internet at all on my phone. I have deleted all recently installed apps, cleared my cache ,cookies, history etc and performed a restore and it is still there. Anyone have any ideas?