I'm trying to advance to warlock but am told that i "don't meet the requirements" by all guild leaders.

My mage skill levels range from 33(lowest) to 72(highest) and I have paid the required guild dues.

My intelligence and willpower are both 70+ and I have done all quests assigned to me by all of the

guild leaders. Can someone tell me what I am missing?

If you hover over the Mages Guild entry in your character box it should show what you need to advance.

Though if you have a mod that adjusts faction advancement, I don't know if the window would reflect that.