Hi Kourtney,
I am sorry that happened so soon in your hosting experience 😞 However, I just wanted to add that calling the police (unless someone is threatening you or harming you or tearing up your property and refusing to leave) is rarely a workable solution. Police just have no authority to handle Airbnb issues concerning guests or uninvited guests in a business transaction. It's a civil case and rarely do they want to be involved. And it's not a good idea to put yourself on the radar at the precinct in that kind of way.
I recommend writing in your listing that all guests (at all times) must be registered guests on the reservation to access the property in order to adhere to insurance & Airbnb policies and regulation - and of course, for your safety. You can then point them to reading Airbnb guest policy where this is concerned. This information is clearly laid out within the platform rules.
I would also state the consequences of breaking this agreement on the final line - something like, "allowing guest who are not registered on the reservation to access or stay on the property at any time will result in termination of the entire reservation and no refund will be given."
Airbnb will back you up on this every time - because breaking house rules is a no no, whatever they are - is your ongoing right as a host. Your place is not a hotel, although some will mistakenly perceive it as one.
When guests break the house rules, many times, they are conscious of it and will test your boundaries. Having guests in your property that are not registered - are not covered, and if they break something or get hurt, that could become a real problem for you. As hosts, this line of self-employment requires a strong sense of assertiveness and the ability to recognize and act on the messages coming out of your 6th sense. Your inner wisdom to detect and trigger the actions needed to eliminate problems before they get out of hand will become stronger as you go along.
Lastly, feel free to read my listing. It helps a lot to be as clear as possible beforehand, so in the event of a breach of agreement, you are covered. I'd be very careful of tolerating guests until the end of their stay - who blatantly disregard the agreement, because in my experience, when they do break rules, they go on breaking more and more..... and in the end, they will reward your patience with a bad review or worse.
Just nip it in the bud - and spare the local precinct the drive over for situations they are not equipped to resolve. Best to you.