Don't use fly spray, it doesn't work well on fruit flies. Get a couple of glasses, add a few cm of cider vinegar, wine vinegar, or even cheap red wine (it all works, but cider vinegar works best I find). Add a couple of drops of washing up liquid. Cover the tops of the glasses tightly with cling film. Prick several small holes in the cling film with a fork.
Fruit flies can't resist the smell of the vinegar and they'll climb in for a drink. They can get in through the holes but can't get out of them because of how they fly. When they go to land on the vinegar they drown because of the lowered surface tension. The glasses will be full of flies in about a day or two and your problem will be gone.
Make sure to always rinse out your used beer bottles to stop them coming back. Beer is a magnet for fruit flies as you're finding, but stale beer (even a couple of ml) even more so.