Why is my phone not turning ON?

Recently i was recording a video at 4% charging and soon after recording that i put my phone in my pocket but when I took it out, it was Off and wasn't turning ON (so I thought it might have discharged) But even after plugging it in for charging, it still won't show any response. I did try to get it checked from a local technician which said, it had a mother-board issue, and its Power IC needs reballing but even after trying to reball for 3 times the phone still didn't turning ON. Any ideas what the problem could be and how can I get it fixed. My phone contains some of my very important data so at the very least can I get my data back?

If I remember correctly, it all started after I had an issue with the front camera not responding, most probably that started after the update.

P.S: I have never charged my phone with the charger other than the company provided one and nor did it fell down or did it come in contact with water.