Genius bar cheating customer

I had a small problem (little a yellow spot) on the display for few weeks on my iphone, so I made a appointment on the Genius Bar Carrousel du louvre Paris, (my Iphone 7 plus only bought 6 month ago) and a technician checked my phone, after they open my phone, said its because the water damage, and its not cover by the insurance. i have to pay 400 euro to change it, so I didn't agree that then I left without fix anything , but when I left the shop i found my phone is not working and then i restart my phone the display is totally black. so i went back to the shop, and ask if they did something wrong when they open and check my phone to cause my phone totally broken? but the technician refuse to check my phone again and insist this problem is because the water damage they can't do nothing, and he just walk away left me leave me stand there alone?! after 20 mins finally there is anther guy come to me but still refuse check my phone and say they did nothing on my phone and the only way i can do is to pay 400 euro?!

so i left the shop ask my friend who is also technician, and we found the screen did not well plugged, and he just replug it, my phone works very well. there is nothing about the water damage.

I highly challenge the Genius bar louvre broken customer's phone in purpose and charge more money! and we come to the Genius bar to fix our phone not broke it! this kind of deception i can't believe is happened in Apple this kind of company, i feel so shame for you.