@Halima17
It is ridiculous but you are the master of your ship - not your guests - and unfortunately you are enabling them to carry on with this behaviour.
You have stated in your house rules no visitors - you have all the resources you need BUT you do need to enforce the rule or guests will walk all over you - as they are now!
As soon as you saw the extra people you needed to remind the guest of the house rule that he agreed to when he made the booking.
You could say Hey XX I'm sorry, I just can't have extra visitors. It's an insurance requirement - having extra people here violates my insurance and also violates your airbnb stay. Strictly speaking I should ask for your stay to be cancelled now, but I'm not going to do that because I'm such an understanding person and i'm sure it was a genuine mistake. But I'm sorry, your guests are going to have to leave. Whether you realised it or not, this is what you agreed to when you booked my place" Then immediately ring Cs adn get your version recorded in case there is a complaint. That's what you should have done IMO.
For now, you can do pretty much the same. go out now and say - you were taken aback by the extra guests - you've contacted your insurer and you've contacted airbnb and he is violating your terms and conditions, AND you are just not comfortable with extra people in YOUR home. Get them out, then ring airbnb ( or ring aribnb then get them out), but take affirmative action.
You don't need to be rude, Blame the platform rules, blame your insurance rules, so that it's not personal, its business.
Good luck!