Iphone 6 being so weird I really need help

iPhone 6 turn off and show weird color and I cannot open it for a long time. I broke my last iPhone 6, and I went to Apple Store to fix it. But they cannot fix it so they told me to pay $299 in order to get a now iphone(btw it was screen and camera). So I got a new iPhone but it stared to show weird colors and turn off suddenly. I cannot open it for a long time. What should I do? I got this phone for like 3 weeks. Did the Apple Store gave me the broken one?