Shutting it off at the tank should have stopped the flow. So the tank valve must not be sealing completely either. Your float valve isn’t shutting off 100% as it is supposed to. But expecting it to shut off completely overnight may be asking a bit much.

Is your cork float in good condition? It may not be bouyant enough. Or there may be a micro defect n the float pin or it’s seat in the bottom of the bowl. Some suggest lapping the pin and seat with valve lapping compound, and I gotta admit I’ve done it too. With mixed results.