The Chaos Servant Convenant is actually hidden quite well if you don't know where to look. It's located just past Quelaag's Domain underneath the second bell. You need to get to Quelaag's Domain and defeat her to access the second bell. Go to the lower room using the stairs or the hole in the floor, and hit the false wall. You will see an egg man, but do not attack him. Talk with him, then he will let you talk with the White Spider. If you don't have the Witch's Ring, you don't know what she says. Either way, speak with her to join the covenant.