Blood elf warlocks cannot summon imp

I need help，I'm a blood elf warlock，now I'm level 70，but I still can't get the task of learning to summon imp，I know this task was learned in the birthplace，but the NPC doesn't give me quests.And I realize I'm not alone，all blood elf warlocks cannot summon imp.I submitted this error in bugtrackr, but it shows Dismissed.

Try the trainer. It costs 1 silver to train it.

I ups a 3 (1-52lvl) elves. Not one could not make a imp. Thanks to the admins of the server. On the ticket just ignore. Im in cry. I spent the whole month on this question. I read all the quests on wowhead.