You would probably need to fire it before they activated the skill and the range for Fear is less than the range for most gap closers.

Unless Fear can also be used as Interrupt, but then the question becomes can you Interrupt a gap closer?

As far as I know, there isn't a way to do this in the manner you've described. I suppose if they are close enough to you then you'd be in range of fear, but even if it's cancelled you'd see the visuals coming off of their character.

I'd like to see this in action. Any way you can provide a video?

I have never heard of what you describe, but is it possible it can be attributed to lag? To my knowledge it is not possible to animation cancel fear, plus if he does a fear followed by a charge, then he is too far away for the fear to hit you before he charges. So the likely scenario is that he is charging you, then fearing, but as @Autolycus said, it would be nice if you had video footage to back this up.