I think you need to mix it up a bit, it's like they get use to products so you need to change what you use.
We use Ya Mate
https://www.loveoilco.com/products/2/Ya-Mate_Insect_RepellantA Birdsville local put us onto Nature's Botanical, like he said it stinks but they all use it so they stink together
http://www.naturesbotanical.biz/products.htmlThey drink Areoguard. Also use the insect repellent OFF. That seems more effective on mossies than flies though.
Fly Hat a must. You can buy nets that go over your existing hat, only a few dollars from a junkie shop.

I made this to really get away from the flies I bought a large mozzie net you put over a bed, sewed fishing sinkers along the bottom to hold the net down and in place and throw it over a beach umbrella, held in place by some velcro on the top. 2 seats can fit under and it works a treat, quick to set up and gives us a reprieve from the flies.

Personally don't like the ones with high DEET in them even though they do work.
Good Luck
