You can always complain. There is nothing to stop you.
I am sure Citi is going to credit you regardless.
However, to get the record strict, your CC's T&Cs does mention that the exchange rate is based on the wholesale price by Visa/MC/AMEX, which is something like this:
http://usa.visa.com/personal/card-be...calculator.jsp
And your exchange rate is based on the transaction date, not posted date.