The mosquitoes are driving me crazy

‌The autumn mosquitoes have been so aggressive lately.
I live on the 11th floor of an apartment, so I have no idea how they get in...
I estimate I'm killing at least 10 a day.
But when I try to catch them with an electric swatter by following their flight path, they suddenly vanish right before my eyes.
It's amazing how they can do that.
If I fail to catch them, they show up right when I turn off the lights and lie down to sleep with a "buzz~", driving me absolutely insane.