It sounds like you’ve covered the bases.
I’m suspecting the charging logic is damaged so the system is not getting power. Basically you have a set of MOSFET’s which act as switches between the MagSafe & battery with the systems logic. These MOSFET’s can get damaged from static discharge or a knockoff charger.
The logic board can be fixed or you could just replace it. But you’ll also want to get a REAL Apple charger directly from Apple. Don’t fall of the ‘OEM’ or ‘real Apple’ monikers you’ll find on Amazon, eBay or other non-Apple source they are most likely setting you a knockoff.