Phone won't turn on or charge at all!

Few days ago I found my phone off in the morning. I put it on charge for whole day, but it won't turn on. When I try charging it (using it's own charger) , the charging indicator shows up, but percentage stays at 0%. I tried charging it using PC, but in vein.

I tried using an external battery charger. Even if I charge the battery to 100%, it drains to 0% withing 5 minutes and turns off.

The repair shop I took my phone to assumed it has a problem in charging IC(since they said there's no problem in battery) and changed it, but it didn't help either.

Normally if I press the power button, the display screen somewhat glows up, but remains black and won't turn on.

Please help me. TIA!