Airbnb Violation of Contract and Airbnb Gave them Refund Internet

 I confirmed one guest to stay at my condo.  This is essentially the contract which is established between said guest and myself.  She arrived, but later that night (at 10pm) she let her 18 year old son into my place.  Airbnb said if I cancelled her reservation for the subsequent night that I would be penalized (I wouldn't get paid for the night they already stayed + I would have additional penalties).  They said she was allowed to bring her son because it states in my profile that I can sometimes take 2 guests.  I protested that what is possible doesn't matter - what has been agreed and signed on is the only point of validity.  The woman stood her ground and was very adamant and unfriendly stating I would have monetary punishments and since I have it as a possibility on my profile this is equivalent to having accepted the son....   I am very surprised at this threatening behavior on the part of Airbnb.  They did not care about my wellbeing, but evidently did care that they would get the percentage of the rental and would try and threaten me to ensure they wouldn't loose that.... I didn't want this guest to continue staying - I was uncomfortable and I felt unsafe with her.  She was manipulative, disrespectful guest and she refused to return my key until she had a full refund.