Phone won't turn on after charging port and battery replacement

Okay so I had this iPhone 6+ that would die really fast. Like it would be at 1%, I would plug it in and in a minute the battery life would display 100%.

I first replaced the battery. After the battery replacement, the phone turned on for like 15 seconds showing the Apple Logo. Afterwards, it turned off completely and never turned on again. I tried replacing the charging port as well to see if that was the problem. However, nothing happened once again.

I have an original brand new apple charger so the charger is not the problem. I have tried to put the phone in DFU mode and Restore mode and nothing happens. iTunes does not recognize the phone at all.

Any suggestions?