[Xperia XZ1 G8342] Phone overheated and doesn't turn on at all

I literally made an account here because I've given up searching. A brief context, I was ordering food on my phone and noticed it was 15% -- No big deal, just charge it right? after charging the phone overheated very quickly, I unplugged (its still alive) and cooled it by just putting a damp cloth on the back side. Once it cooled off, I plugged it in and it dropped from 15% down to 3% then completely blanked.

Went to a repair shop and they deem its a dead battery, but they had no available stock locally. They have to order it from a different state (im not from the US.) which they have mentioned will take 3 weeks and their process was ass. I went around to another shop and this guy mentioned that it isn't battery but possibly my motherboard. I kinda shrug it off and was hoping it was my battery only as its an easy fix. Plus he was the odd suggestion after asking 5 more shops, so I leaned on the battery fix.


Got home and ordered it online myself. I waited 1.5 weeks for the replacement battery, oh my phone worked when I plugged the new battery in BUT --> it overheated yet again, didn't even turned it on. I decided to just let it rest on the table. Came back to it (like barely 10mins?) and its very cool now, no signs of life at all. Man, I just wanna get my files out of here and buy a new one :(

The files is what really matters to me. I'd do anything to fix it as long its not an astounding price tag.