Just treating the tops of the plants is not going to win you the war. Neem oil products typically just talk about spraying the tops and bottoms of the plants. Thats where the problem is that they dig down about 2 inches to lay their eggs. THe think the lifecycle for eggs to flies is like2-3 weeks. Now you can get a product like azamaz what gives you intructions on spraying the leaves and then treating the soil and that you need to do it every 2 weeks for awhile to make sure they stay gone. After that if you replace the top few inches with perlite or sand in your pots the mites wont live in those and it should deal with the issue long term. I use azamax myself and do the every 2 weeks thing and it seems to deal with them pretty good.
You can also put a piece of potatoe on top of the soil and they will lay their eggs there so every few days just throw it away to kill any eggs or larva that might hatch and replace with a fresh piece.
