They refused to replaced my phone even it's still ...

They refused to replaced my phone even it's still under warranty. They just make and excused to denied the warranty even the phone was all original. They give me back my phone after they broke the bottom screw bracket inside and they don't take responsibility for that. My phone just had the lines on the screen display but the 2 bottom screws was there before I give it to them, then after 3 hours of waiting, they hand it back to me with 1 bottom screws missing. I ask the guy where is my screws and he went to the back get the screw and give it to me because the tech was broken the bracket inside and can't put it back.
The so call manager name Kelvin was not professional at all and do not take responsibility for his tech did broken my phone. I was so mad and will file complaint with state, BBB and Southlake city about this crappy place.