I would contact the agent first to see if they have confirmation from the hotel of the corect event on the correct night, and see what the agent can do - they probably place a fair bit of business that way so the hotel may want to recompense via the agent. If not, write a formal letter to the general manager at the hotel saying that you did not get what you booked for, and asking for a refund (unless you enjoyed yourself anyway, in which case ask for a partial refund or other recompense). Did they confirm in writing to you what you were expecting to see? Don't forget, it might be the agent's website which is incorrect, not the hotel's?