hotel bill dispute

Hallo
I booked a hotel in Prague online through Haystack, the Lonely Planet booking service in November. Haystack emailed me my booking confirmation stating how much the accommodation cost and how much was left to pay at the hotel.
At the end of our stay we went to check out and the receptionist gave us the bill which was more than that on our confirmation.
We showed the receptionist our confirmation and she adjusted the bill to the amount on the confirmation.
Since coming back from Prague, the hotel has debited extra money from my card saying that we didn't pay enough.
The hotel has mailed me informing me that the receptionist should have charged us more and that they have taken it from my credit card.
I mailed them to explain but they replied saying that Lonely Planet had made a mistake and the amount they have taken is correct.
Can they do this? Didn't I enter a contract agreeing the price when I booked through Lonely Planet?
Hope you can advise me.

Yes you did--and Lonely Planet should pay the for the error.

You are entitled to rely onm the fee you were quoted.