My iphone screen is going crazy after I had it fixed?

I shattered my iphone screen a week ago and had it fixed at a local shop (not an apple store) and it was repaired the same day. I noticed that evening that there where five or six thin white lines running down the screen diagonally, but I ignored it because you could only see them if the screen was at full brightness and there were dark colours (like in the compass app). But last night there were horizontal lines of colour all over my screen (mostly pink) and they were messing with my display, they're worst on bright/white backgrounds and they were sort of in swirls and kind of pixelated? It's hard to describe. That came and went until tonight, when it got so bad that it was everywhere and my phone started going crazy, like my display faded into horizontal lines and shook but went to black and the screen was unusable, so I turned off the screen with the power button. Five minutes later I turned the screen back on and it was just the colours again (but still really bad). The screen is still responsive, I can still tap away until the next time it freaks out. I haven't had it near water or dropped it since the repair. The repair was actually the first time anything's ever happened to my phone. Do I just need the screen replaced again or is it a software issue? I clearly don't know what I'm doing here, so a simple explanation would be great. Also how much would it cost to be fixed? My contract is finished in November so should I just wait and get a new phone?

Take it back to where you had it fixed and get the screen replaced again under warranty - you paid for a new screen & it's faulty, simple as that.