Bank Account double charged

On 25th May 2015 I purchased airline tickets online. The payment was confirmed and deemed successful by email from travelstart. I was issued my electronic ticket. On the 28th I was charged again by Singapore Airlines for my tickets from my account. By Friday my bank account was R19 876 in arrears. Due to being charged a second time for the same tickets. I was told by travelstart that the problem was with my bank. How does a bank create a debit order on behalf of Singapore Airlines. I can't use my account even to transfer money for personal use and I have to wait 24hrs for the bank to do a reverse of payment. If it was just a bug then my bank could clear the problem immediately but my statement clearly shows I was charged twice by the airline that was arranged through travelstart which I entrusted my banking information to. I have booked many tickets online before with other websites and this has never happened to me.