booking.com stole R18,000 from us

In August this year, we made a hotel reservations in Durban through my girlfriend, booking.com took the sum R18,000 from her account as security deposit. We spent 2 nights at the hotel, cleared all our bill. But till date, booking.com have not returned the R18,000 they took from my girlfriend’s account. It’s over 3 months now, and they are not saying anything reasonable concerning that.