FNB Card division over charged me when I bought $

On 10th December 2015 I made an online transaction buying US$300 and same time I have received SMS saying: FNB:-) P3357.84 reserved for Purchase @ www Nymgo com from FNB card a/c.. 651000 using card.. 1020. 10Dec 08:39 and on 14th December above statement changed to: 10 Dec 2015 WWW NYMGO COM LONDON W1B 5T -3,498.86 in my bank statement. I have contacted FNB card division and according to them FNB doesn't have any access on exchange rates and it is done by VISA department. I have checked the visa official site and the exchange rate on 12th (Transaction went through as per FNB) is: 11.350<br> <br> How dare FNB can charge me P11.662 per US$ on 12th December where the actual exchange rate is: P11.350 per US$?