How can I get Comcast to fix my connection?

I've been having connection issues for about 6 months. It goes down for about a half hour every day and I've had probably 10+ techs out from Comcast over this time. They fiddle with some wires, then go away and since it is always working when they show up, and when they leave they think the problem is solved. Obviously it isn't, I don't know what is causing this, I just want it fixed. Can anyone provide experienced based advise on how I can effectively navigate the Comcast bureaucracy to find resolution to my problem? FYI I live in an apartment building in downtown Chicago, IL.