international word for "NO!"

Have you ever been in a hotel room and forgot to put the "do not disturb" sign on your door? Of course at one point in the morning the housekeeping women are coming. I think word "NO!" means the same in english and spanish and I guess in a lot of other languages as well.
So my question is why do those women always pretend that they don't understand what you want from them?
Last night I forgot to put the sign on my door. But I locked it from the inside. This morning the housekeeping women tried to get in my room to do their job. I woke up by the loud noise that a locked door makes if somebody tries to open it. At this point the women should have noticed that maybe somebody is still in the room. There must be a reason why the door is looked. But instead of going to the next room and coming back later to see if the guest is still there, they start to knock on the door.
WHY?
At this point I was awake and kind of angry. So I went to the door and opened it. I saw to little women which seemed very surprised that somebody opened the door. They looked at me and in the very same moment both of them asked: "Housekeeping?"
I anwered: "No! I'll leave the room at 12."
They looked at me and as if I didn't say already NO! they asked again: "Housekeeping?"
This time I just said: "NO!"
Of course they asked again. But then I had brilliant idea. I showed them the "do not disturb" sign and put it right on my door infront of their eyes. If this is not crystal clear...I don't know.
Both of them still looked at me and asked: "No housekeeping?"
Sorry, but which part of NO! you didn't understand in the beginning? Was it the N or the O?