Problems with booking websites

I wonder if anyone has had this experience with Booking.com and did you get any satisfaction? I booked a hotel in Dublin through them and perhaps unwisely opted to pay when I arrived in sterling. I questioned this being much higher than a) first estimated by Booking.com and b) much higher than the average exchange rate. they said it would be my bank which decided this but I have twice been reassured by my bank that as nothing was converted by them (I opted to pay a euro charge in sterling) it is the hotel's bank at issue. The hotel is apparently disputing this as every few days I get an email from Booking.com asking for yet another piece of information, copy of bank statement etc etc I have already sent them. It's as if they are playing for time. How can this hotel and Booking.com not know that if nothing has been converted it is the Irish bank and fees charged which is problematic, not mine? I reckon to be out of pocket by about £50.

Glad to get any views.