I've completed the restoration ritual spell quest and gotten the Bane of the Undead spell, but Collete wont sell the Guardian Circle spell. I've tried turning off my xbox and turning it back on, tried activating the augur again, but he doesn't do anything, waited for her inventory to reset multiple times, and gotten my restoration to 100. These are all things I've heard worked for other people to fix the bug, but so far haven't worked for me, has anyone else had this problem and found a way to fix it?

I had the same problem.When i had to survive the fight against the 3 ghosts i had a follower with me,and when i finished and went to Collete she didnt have the spell.I believe i loaded an earlier save and re-did the entire quest without a follower and then the spell showed up in her inventory.I might have also reloaded the part where you talk to her to finish the quest to get it to appear,can't quite remember as it was a while ago.Hope this helps

Thanks for the advice it finally worked after re-doing it a couple time, looks like you just have to keep doing the ritual quest until she decides to sell it, the whole quest still seems glitched though, like after i finished it the augur wouldn't stop repeating that line he says after you finish the quest and the quest completed sign kept popping up.