https://www.rentalcars.com - No assistance with issue!

I have made a booking with Rentalcars .Com for a car rental with Hertz. My pickup was on Sunday 10 November 2019. I paid the full amount of R 2800.00 for six days. O(n the pick-up day, they requested a R 16000.00 on my credit card for insurance. I had more that that available, on my credit card, but my bank refused the transaction. As it was a Sunday, i could not resolve this issue with my bank and hasd to abandon the attempts and use Uber. Not being able to use the service i app**** for a refund. I get no response from www.rentalcars .com. Is this legal according to the consumer act? I will have to pay a visit to my layer to resolve this.