Call a manager back during regular business hours when you are back home and not calling from an airport gate. Leave out all the irrelevant stuff about behavior and stick to the simple fact that you did not use the item and thus did not damage it in any way and thus any damage must have been pre-existing. Obtain the manager's name and email and follow up with an email to her. Again, keep it simple and short. They know exactly how often you have stayed there and whether you have had other incidents.

If that doesn't work, you could try a chargeback dispute for the $300 and hope that the property does not respond to your CC issuer. But, it becomes a "he said - she said" so don't put your eggs in that basket.