Rentalcars.com dissapoints

I booked a car for 3 days through Rentalcars.com and paid them. On the day of picking it up the rental company Thrifty told me that they do not accept my debit card although I called them prior to my departure and the gentleman I spoked to said the debit card will be accepted I only need to make sure that I have a deposit of R9 500 available on it which I had. When I wanted to pick up the car they refused my card. I was left stranded and was filled with amanxiety, frustration and anger. First Car Rental came to my rescue and offered me their rental car. I emailed Rentalcars.com and informed them about what happened. They told me I was supposed to call them from Thrifty's desk than they were going to refund me. How was I suppose to know that if they never informed me? They now refuse to pay me my money back after I've been a loyal customer to them for a while. I'm so much dissapointed in them and will recommend people to never make use of them.