I used to be a comcast customer before I relocated to Florida. They have done similar on more than one occasion to me. I had one day where they missed their window, but the woman on the phone told me they were still coming......I waited, and 7 hours later, there was nobody.
Repeated complaints to their phone support/service people went without help, and the supervisors/managers would not return voice messages. I voiced my complaints on this forum (AVS) under the local cable companies section and surprisingly I had a senior Comcast administrator give me his phone number (from Delaware) and I was from Pennsylvania. He monitored the AVS site for comments, and had seen my complaints.
I called him, and within 2 days I had a local manager call me and by the next weekend, had my problem fixed.
My advice is just be persistant.......not all comcast employees believe in bad service. (although in some areas it does seem that way). I now am using Brighthouse cable in Florida, and so far, I am pleased with their service.