That truly sucks. Sorry man. My only suggestion is in the future, whenever you make a change in your reservation, and especially if you shorten a stay, arrange your schedule to physically check out of the hotel on the last day and get a receipt. It is infinitely easier to resolve issues while at the hotel than later. For example, had you been presented with the higher bill, you might have said, screw it, we will stay for the 5th night even though no one will be in the room. Not this specific case, but whenever you get a long term rate, it pays to check the daily rates. A $150/night rate might actually be $175/nt for the first four nights and $50 for the last night. Any number of permutations is possible.