Screen picture problem after a new screen. New screen or bug? Help

Had my iPhone 4 for 18 months. No problem. Dropped and smashed it at Christmas. Sent it off as per insurance for a new screen. 2 weeks after getting it back it started. It suddenly goes as it the picture is slightly too big for screen. Then it will go where i can see all the icons. Some faintly in the background. Ten it will go off. Black screen with white lines down. I can hold the top button down and just see the red of the swipe to switch off button which I can do then sometimes it will come back on. Other times it takes 2 days to go back. It's happening more frequently now. What is it? Is it related to new screen or a bug? Help.