Nostalrius Begins - Quality wow vanilla realm (1.12)

I have the item for the quest called "Taramagan the Hungerer's Heart" and the quest is logged as "completed" but I can't turn in the quest. Would love to get some help with this.

Name: Onslow

Abandon the quest and pick it up again to turn it in. You will retain the item in your inventory and it will be completed after you pick the quest up again.