Authorised money not returned and overcharged on vehicle hire6

Last Sunday they took R7500 for authorisation and still it was not given back. Although it says the the moment the car is returned it will be revesred. My account was R422, yet they subtracted R1800 from my card. With no explanation. Second time I have to ask for my money back from first car rental. Very disappointed. FIRST CAR RENTAL ********** 5 COERTZEN C miss **********