Greetings Darkius,

I’m sorry to say that these forums aren’t the best place to report a situation such as this, as we don’t deal directly with any in-game issues here.

I notice that you also submitted an in-game help petition about the matter, however, and that the representative who spoke to you was able to explain that the reason you regrettably didn’t get credit for this achievement was because your character died during the fight, rendering you ineligible by design. :(

I do hope that you’ll have more luck on your next attempt though – fingers crossed!