I think my agency may have paid me incorrectly for holiday pay

I am an agency worker working a contract at present for 8 months. I have accursed holiday of which I have taken two days (one of which they failed to pay me on time for). On receipt of this weeks wages I was advised I would be receiving two days full holiday pay. When I checked my payslip this seemed to be quite a low amount for the days I had asked. My normal working week is 37.5 hours with an early finish on a Friday as defined in my contract, my two days I requested were a Monday (bank holiday) and a Tuesday a few weeks ago, my agency have said that they have paid my holiday correctly but I am not convinced this is correct, I believe that they may have paid me for a Friday rate as opposed to my normal working hours. Is there any way I can check and confirm that my instinct is right and what can I do to claim the full entitlement of holiday I've accrued bearing in mind my consultant will be getting commission with me being in my current position

Isn't the simple answer to talk to the person that is responsible for accounts payable and come to an understanding on what the correct amount should be?