Just give my money away even if I don't have it

I recently purchased 2 airline tickets through [URL Removed] for my wife and son to fly from JHB - Miami - Nicaragua - JHB. I paid +-R35,000 for these tickets and had a few thousand Rands left in my account after the purchase. 3 days later I am charged an additional +-R35,000 (two separate amounts) for the same air tickets thus putting my account way in to the negative balance! First of all, After trying to reverse the double charge I was told \its already been banked by their side and I must contact the merchant"How the hell can you firstly allow a purchase that will put my account in to the negative by tens of thousands of rands with no overdraft facility and secondly you still have the cheek to charge me fees for having a negative balance! I am very upset with this whole situation to see how my money has so easily slipped out of my account."""