How do I Request Line Maintenance?

I'm at my wit's end with troubleshooting a recent internet issue. I posted about it at length here, but the Xfinity rep (@XfinityRobertA) in the replies never responded to me, and I also tried sending a private message, but never got a response. I have a brand new line into my house, brand new modem, and the same issues I had at the beginning are still happening. If Comcast can't fix this, I will unfortunately have to consider switching providers. I work from home and can't afford daily internet outages, not to mention the headache of constantly troubleshooting. 

Since the new line was run, I was told that if the issues persisted, the cause probably lies outside my home somewhere in the neighborhood lines. How do I escalate and get a crew to further inspect the lines?