Why did my phone turn blue then black

A

AC Question

I have the Samsung galaxy s6, i got it at after the release immediately. I'm a clumsy guy and over the year and a half that i owned this phone i would drop countless times and it always came out as a champ and would be perfectly fine until one day i noticed there was a small patch area with blue on it so i thought it was a glitch so I turned off my phone. after about an hour or the entire screen was a light purple blueish colour and it was starting to spread. So I decided to go to fix it at a local mobile place and they fixed it for about the equivalent to 200 USD and everything was fine for a week. Until it happened again, same thing a small blue-purple area and then it spread. I feel like i was ripped off, because i told the guy that i had this phone for about a year an half and never experienced this issue and then all of a sudden after you fixed it it happens again after a week. He said that i dropped and he pointed to a small scratch on the screen and blamed it for the issue.
Since fixing the phone it only dropped once which was off my desk to the rug and i am pretty sure that after such a small hit like that the problem would happen again. Please help me because i feel that something is not right with the guy that i fixed it at.

I appreciate your time