Serious problem with Expedia.com

I've made a flight booking from Singapore to Calgary few days ago with Expedia.com, and received Confirmation immediately after everything. After a short while, my bank called me and said the transaction is not successful and being rejected. I've called the bank twice between day and night time and I received the same answer that was Failure Transaction, and I have to make a new booking as the 1st transaction is not valid.

Therefore, I created a 2nd booking, the transaction went through and I received another confirmation as well. I called and checked with the bank again and they said the transaction went through and it's Confirm. After that, I sent in email to double check with Expedia.com, they said they have limit service in dealing with email, they asked me to call the service center directly.

I called, and being talk and hold the conversation for almost an hour (well, 50mins perhaps), they said it's my fault in making duplicate booking as the 1st one is already confirmed. They said the transaction was being done and confirmed, the Delta airlines has already reserved the seat (for the first booking), they will refund me money for the first booking, and also CHARGE ME SGD250 for changes or whatever fees then~

I called Delta Airlines, they said they will cancel the flight without charge me anything, it's Expedia.com itself to CHARGE me as I booked with them instead of the airlines directly.

I am so pissed and is there anyone can tell me what's going? I wonder how the Expedia is going to charge me whereby the first transaction (with the first booking is not valid and not going through with valid payment)? and I wonder why they said Delta Airlines is going to charge me for flight cancellation? IT'S RIDICULOUS~!!!!

May I know what can I do?? Please, if this was solely my own fault, I am willing to pay for my mistake, but not with such RIDICULOUS REASON~!!! HELP~!!!