Oooh I had this problem...
If you have a garbage disposal....clean it! You can actually buy garbage disposal cleaner, it is a liquid you put in, and it foams up when you run the disposal, works like a charm and no sticking your hand down there. I thought mine was clean and that is where they were coming from. I used those sticky tape things you hang, they worked well. Eventually I just bombed the place and that solved it.
Just clean everything, no food can be left out while trying to get rid of them, no crumbs and nothing spoiled in the fridge.