I wanted to thank everyone for help. I will keep everyone posted about the developments. Hopefully, this time I will really receive the refund and Comcast's records will really be updated to show that I'm no longer their customer. And I also hope that they find out what went wrong, so that other customers do not end up in the same situation.
In addition to emails and phone calls to me directly, Comcast (more specifically Frank Eliason) responded on The Consumerist article: