It could be a food intolerance! I had the exact same issue!!! i used to work out tonnes, tried dieting, calorie counting, the works! And yet, I seemed to be unable to loose weight! Worst of all, it all settled in mostly my belly. i continued to look relatively scrawny with a huge belly.
Then I read Wheat Belly and it changed my life. I went gluten free, and within 3 months I went from 72 Kilos to 65 ( I can post my fitibit aria measurements here if you like! i still can't believe it when I see it!). Then I reduced my dairy intake and added yoga to my workout routine, and now I hover between 61-62.5 kilos (i seem to have platoued here, so i'm changing up my workout now to be less weight loss and more toning/muscle building in the right areas to boost my metabolism, as my belly is not as flat as i want it, but pretty darn close).
I also find I can cheat quite often, and as long as i'm staying active it comes off within a week, something that certainly did not happen when I was on a gluten diet. Some people might balk at this whole "gluten-thing" but I can say it doesnt affect everyone (my wife quite happily eats all sorts of gluten stuff). but based on personal experimentation I have an issue, as any attempts to consume gluten again have resulted in major weight gain in the belly area.
As such it's the first thing I recommend when people are having trouble loosing fat specifically in the belly area (as based on my reading this is where fat likes to go when plagued by a gluten intolerance). Try it out for a month and see if you notice results. If not it's probably something else (maybe dairy?)