so, you had an oral contract to rent this property and you agreed, when you paid the deposit, that it was a non-refundable deposit, right?
and now you want them to refund the deposit although it is less than 6o days before the time you chose and scheduled, right?
so, you figure they are just supposed to take the loss, right?
I would suggest, if you cannot use the time you either find somebody you know that might want to take your place or you ask the proprietors if they would refund the deposit if they are able to re-rent the place for the time you had reserved.