Eskom's R78 000 billing error

They disconnected our home due to their own billing error. They now expect my mother to pay R78 000 due to that error. Two weeks ago they were supposedly going to investigate so they reconnected her. Now all of a sudden with no plausible explanation, they're demanding payment and threatning to disconnect her again. None of them can offer an explanation for the error yet they're demanding R 78000.