Fruit flies (together with other organisms) are a part of vermicomposting to a lesser or greater extent. We can avoid reproduction of fruit flies in your wormery by covering the surface of the compost with your Moisture Mat. You can cover the newly added food a little or possibly cover the surface with already processed compost.
You can also create one of the recommended traps. For example, you can put a piece of banana at the bottom of a jar, create a paper cone with a tiny opening and place it point down into the glass, sealing around the edges. Or mix 3 tablespoons of water, 1 tablespoon of vinegar, 4 drops of dishwashing liquid and a pinch of baking yeast and place a container with this mix near your wormery.
If the flies do hatch, they don't get out and that can be a success. Unfortunately, you may repeatedly introduce the flies into the composter with fruit and vegetable peels containing fruit fly eggs.
Alternatively if you feel the need to start again, our Wormery Rescue kit has everything you'll need to give it another go. https://www.wigglywigglers.co.uk/wormery-rescue-kit.html