**** they *****ing my money because they have my card details

They are ****, Nissan rented a car for me from them on the 20th of July 2018, I was asked to give them my bank card so that they can reserve petrol money which was R600. When I returned the car they already took my R600 so decided not to pour petrol on their car. Now every month since then they are debiting me over R600, I am not even their client.