Who is There?

A sudden storm brings an unknown, unseen caller to my door.

The hour is half past ten PM. The sky is dark with storm clouds, gathering overhead. The streets below my room are almost empty. The wind is high. At first, I hear the  loud rush of pouring rain from my window. A thunderstorm has brewed. I recline in my room and wait for it to abate. Then, I hear a strange. loud knock on my door. At that hour, certainly, I had to wonder who could be calling me. The knocking continued. Before going to open it,of course, I asked,
"Who is there?"
The knocker did not reply with words. Instead, he or she continued to knock loudly. I became a bit annoyed.
"Listen up! I asked you who is calling. You can't be the police. Nobody has reported me. Tell me your name or I will call Society Security!"
The knocking continued as before. Slowly, my annoyance transformed to alarm. Apparently, my caller did not understand my language, but I doubted that he was a foreigner. I knew that neither my acquaintances nor the police could be at the door, because they would have identified themselves to me. And strangers never call on me at my room. Slowly, I opened the door wide enough to look into the corridor outside. Thunder clapped in the distance outside and lightning flashed, briefly illuminating the corridor with a faint glow; but it disclosed nobody.  I concluded that the caller was a prankster a nd he had run away. I closed my door and sat down. A few minutes later, the knocking resumed. I called Society Security, who sent an officer to my floor a few minutes later. After searching and inquiring on the floor for about one hour, the officer had to agree that it was a prank. Fortunately, after he left, nothing happened.
Who had called on me? I would never know.