Money

Hi, i payed 4000 in someone's account by mistake, i call Capitec call center and they told me to go and open up a case against that person, can you please help me to reverse my money back, 4000 its a lot of money, and i called that person but she doesnt answer her phone, and i tried to send her message via watsapp she told me to go and reverse that money.. What can i do in scared she might use that money, my numbers are *** please help me...