Not all damages are monetary as one responder seems to imply, and implying one is stupid is a relly good way to make friends, whether it is on a discussion board or in person. Poor taste and rude!
That said, is it worth going to the amount of trouble this will entail? Of course you are right if what you say is indeed what you have. It is a 'contract' even it lacks all the leagal jargon associated with a formal contract. Speak with the owner, explain your position and ask if the young woman you spoke with failed to notice your existing reservation.
If this approach does not wprk then it looks like you move or take legal action - which will likely result in your winning in the short but losing in the long terms.
