phone not responding after battery replacement

Hi all,

I have been experiencing issues with my iphone 6. Firstly, the screen has been a problem as the colors have become over saturated/dimmer and I am able to see the keyboard faintly no matter what I have open. Also, I usually have to unlock, lock then unlock the phone again for it to respond to my finger.

Secondly, the battery life completely dropped off and barely holds a charge so....

I replaced the battery, thinking mine might be slightly swollen (went to the apple store etc etc totally no help). Although this fixed the battery life issue the screen was still as messed up as previous...however, after working great (battery wise) for about a day and a half, my phone went black as ~7% battery left. I immediately plugged it in and straight away the white screen appeared with the apple logo. This remained for a few minutes before returning to the black screen and then begin to switch back and forth every 30 seconds or so. I plugged it in and the computer does not recognize the phone...

I tried the hard reset etc. took it in again to the apple store and nothing from either...completely unresponsive...

Anyone have any ideas on what might be the problem?? Would really love for this to not be the end of the road...

Thanks!