>>>when i looked on fx currency converter
The currency conversion was done by Visa, who want to make their own profit. Ulster Bank also want to make a profit as well, so
this is the calculator you should have used:
http://www.visaeurope.com/en/cardholders/exchange_rates.aspx
Enter the currency conversion rate as 2.65%, as that's what Ulster Bank currentlycharges. (It's actually 2.65% plus 75p).
(Ulster Bank information sourced from here:
http://www.ulsterbank.co.uk/ni/personal/daily-banking/current-accounts/useful-information/debit-cards-abroad.ashx )
Using today's date I get €599 = £507.46 (+ 75p, as above, = £508.21). Adding on the £23 brings that up to £531.21, which is only about £15 different to the figure you've quoted (and could easily be accounted for daily fluctuations in the exchange rate).