Barclays Credit Card Complaint

Barclays Credit card department,

Transaction issue New York

I purchased - airline tickets on -/-/- at -, i was paying for those tickets - -, the conversion rate on that day for - US dollar was - according to - -, the following day -/-/- the rate for - US Dollar was - -, when i got my statement in the mail I got a whole different picture, the credit card company postponed the transaction for almost a week making the transaction date for -/-/- and the posting date for -/-/-, the conversion rate on -/-/- was - - for each US Dollar, this made the total charge to go up from $2000.00 US Dollars to $2500.00 US Dollars, I contacted the merchant addressing my concern about the date difference and they sent me in an email with all transaction information which clearly shows that the transaction was made on - - which supposed to making it post on - -, I contacted Barclay 's Bank and they instead of fixing the issue files a dispute against the merchant which I never asked, the merchant replied with evidence showing that I authorized this transaction which is true, in their evidence they show the authorization details and there it also says that the transaction was made on - -, Barclay 's Bank accepted the merchants rebuttal and returned the charge to my credit card, I wrote back to Barclays Bank explaining my problem that I am not disputing the merchant but requested the I should be refunded the difference of the - rates which comes out to about $450.00 US Dollars, they denied my request saying that they ca n't further assist me with this issue, I called up Barclays Bank and they said there is nothing I can do to fix this issue and they refused to refund me the difference between the - amounts. I paid for the transaction because I did n't want to hurt my credit history, I never agreed to the full amount of the payment.