HELP MEEEE PLEASE. THESE DARN GNATS!!?

we got home from vacation last night and our hous was full of gnats . we bought so sticky tape and that did not get all of them. This morning i went to buy TAT fly bug killer. We sprayed it EVERYWHERE but i still see them sitting on the wallls so 30 minsutes later i sprayed it again I think it killed some but i still see them sitting on the wall or sitting on the counter then they just float all over the room. Why arent they dying. I cant even eat in my own house. All the windows are closed etc ...... How long does it take for them to die. How does flying bug spray work?