I suspect that this could be one of three issues.
One could be the obvious, a faulty charger or battery. But if you are certain this isn't the issue, then I suspect that it could either be at worst-case scenario a dead motherboard, or if you're lucky, just a bad/faulty DC/power adapter. This would be the female-end port attached to the motherboard that you plug your charger into. Its a cheap part and usually runs between $5.00 to $15.00 at most. Most labor charges for repair are between $90-100.00 at most repair shops so your looking at most between $100.00 to 120.00 for repair. That's worst-case scenario should you opt out of attempting the repair yourself.
(I wouldn't suggest that if you're not a technician).
I hope this helps in some way at least give an idea of what possibly going wrong with your ASUS. I personally use ASUS myself. It's a solid brand. It's unfortunate you are having this issue, but I hope it gets resolved soon. Good day.