GM response long delay and lack of research

This Monday, 9-6-10, my guild killed the LK and I had the quest, the Lich Kings Last Stand. We killed the LK and the sealed chest didn't drop. I looked in my quest log and the quest was complete. We did this in a 25 man raid. I turned the quest in and never got the final rewards. I turned in a ticket and three days later got a GM response saying I didn't have the quest when I killed the LK and they can't help me. I did have the quest and I cannot do it again so I will never get my special items. It was the last quest I turned in and I think it's easy to see I have shadowmourne, killed the LK (with the quest), turned it in and never received my items. I've played WOW since day one and this is the only time I've thought of canceling my account and no longer playing the game. This is a quest line I've been working on for about 2 months and it bugged out and now I'm basically being told to bad and our logs show you didn't have the quest. I don't have the quest now and I can never get it again, nor my items, without blizzards help. This is very disappointing and I don't know If I really care to play the game anymore if I turn in one complaint and get a two sentence response three days later saying they can't help me. Can anything be done?