It’s possible the place you went to wasn’t using or trying a genuine Apple battery (especially if they weren’t an authorized repair facility). Regardless…if they weren’t an authorized repair facility they voided any chance of you getting help from Apple directly at this point. If it isn’t holding a charge and a new battery truly isn’t the solution then that would likely mean something else more significant damage wise. This is assuming you checked to make sure the charging cable and/or adapter you were using were still functioning correctly. Port could be damaged. Liquid damage could have caused internal damage. Who knows. But if you can’t get a real diagnosis from Apple or an authorized repair facility anymore and wherever you took it wasn’t capable of recognizing any issues outside of just being able to open up and install a battery you might just have to get a new iPad.