I've been doing some quests in wailing caverns, and while doing leaders of the fang, I forgot to kill the last boss, serpentis, for his stone. Since i put off my next run of WC for later, I decided to deposit the stones in my bank. Today, I did another run of WC and got the last stone that I needed to turn in the quest. To my avail however, when i went to turn it in, I couldn't, as if I hadn't completed it, despite having all the stones in my inventory. I tried to get some advice on it, and thus attempted to deposit all the stones in my bank and restart the quest. However, even if I deposit all the stones in my bank, when I try to abandon the quest, I still get a warning message that abandoning the quest will destroy all the quest items. I don't know what to do right now.
Please help.