I would suggest that you contact your states Dept of Telecommunication to report the issue as I have had that issue for 6 years and comcast has yet to be able to fix it. I spent one year with their technical people in and out of my house, got to know all of them very well along with the supervisors. It all came down to the comcast network as the issue as it it appears that their VOIP system has some issue at the time of connection. I still have this problem today, so I hate to say don't look for any kind of fix as they yet to fix it in my area.
With a response like that even more reason to report it to your state Dept of Telecommunications. But, I am sure that they still will not fix the issue as they have yet to in my area. Yes, they many reports of this issue over the last several years.