Why won't the top of my screen respond to Touch?

OK so I was using my phone like usual and I was playing a game called Amateur Surgeon 3 and it was working fine I was playing just fine, when I noticed it was getting hard to select a tool, at first i thought it was the app that was failing but later when i tried to use the notification centre. I wasn't able to do this, I turned off my phone then back on but nothing changed and now the top of my screen doesn't work does anyone know how to fix that. If you do please help me fix my problem because I use the top of my screen quite often.