People can book less nights than I put in the system

Hey,

First of all, sorry for my bad english.

I have a big problem.

I put my new apartment here in booking.com. Although I put 7 nights minimum-stay, people can book even 3 or less nights. Now I closed my whole calender, because Im scared, that it will happen again. I needed to ask 2 people, who booked 2 and 3 nights, to delete their bookings.

Isn't it possible, to have a minimum stay for 7 nights, when you just joined booking.com? Any advices?

Thanks in advance