Festergut

Hello! I'm not sure if this is the correct place to post this but I have a problem with getting kill credit on Heroic Festergut. Last week my guild decided to put together an achievement run to get our drakes and indeed it went well. However, there's one problem. I didn't get kill credit for the fight. I put up a ticket and I'm not sure if this is what confused GM's but I wasn't actually asking for an achievement compensation. I was asking for the kill credit. According to this GM "Specialist" They're unable to give me credit because I died on the fight. He/she told me that if you die you don't get anything which is honestly sort of weird =/. They said if you die during any fight you don't get kill credit, or an achievement what so ever. Ok, with that being said why did I get the achievement "Flu Shot Shortage" when he died then? Isnt that a little dumb? You might as well strip that achievement since I died. What I believe here is the GM did not know what he was talking about or he was probably new. I don't mean to sound harsh but I've died many times on soooo many previous fights and gotten kill credit and achievements. I legitly stood on that boss fight, all 99.9% of it until the end. I died due his blight and regardless I got flu shot shortage but not kill credit for him? I only noticed up to a couple days ago that I didn't have credit for him after killing Heroic Putricide on 10man in which was weird and my guildies felt it was weird. We were 100% sure we killed him on heroic. We armoried everyone in that group and yes, it says they killed Festergut on heroic 10 man. So I'm asking this, why am I not getting kill credit for something I legitly did last week? As I stated, I got flu shot shortage that same run so I don't understand. Oh and if this helps the kill and run was on September 23rd. I honestly feel that there's something wrong here. Oh and yes I understand if you release you don't get anything, however I did not release or else I would not have gotten the Flu shot Achievement.