iPhone 6 won't turn on after replacing the screen and the home button.

Hello,

I have an iPhone 6 8GB and about 6 months ago I dropped my iPhone and the screen was broken. I took it to the store were I bought it but there they said it would be more expensive to make the iPhone then to buy a new one. Because I didn't want to spend that much money again I took it to a phone repair shop (Phone Repair Belgium). They fixed my screen and my iPhone was working properly but after a few days it started to behave strange. It started to turn off by itself, the screen started flashing, the home button was malfunctioning... When I tried to reset the iPhone I got the Error 53. So I returned it to the phone repair shop and they said they would analyse it but after a few days they just gave it back and said they couldn't help me and that it was my fault because the iPhone was working when they replaced the screen. I took the iPhone to the store were I bought it but they didn't want to help me because somebody had already opened the iPhone. Then i took it to the Apple Store to send it to Apple but they also wouldn't accept it because somebody had already opened the iPhone. The guy at the store did recommend me to go to another phone repair shop and there they concluded that the home button in my iPhone wasn't the original one. I went back to the first phone repair shop and I said I was gonna sue them for ruining my iPhone and so they just payed back the money I had paid for the screen replacement. Because nobody wanted to help me I decided to fix the iPhone myself, I bought a new home button without the TouchID sensor but it's still not working. My iPhone just has a black screen and it doesn't even connect to my computer (not even after recharging for 30 minutes). I tried all the ways of resetting it with holding the home button down for 30 seconds, entering it DFU mode... But still no luck.

Can somebody please help me?

Sincerely Louis De Geyter