Missing HD channels, major communication issues!

We started Comcast service about three weeks ago in Atlanta and we have had a horrible time getting our HD channels to come in through our TIVO. When the tech came out the first time, he installed the card and said all the HD channels should start coming through within the hour. We start getting basic channels (ABC, NBC, etc) in HD but not the other channels we are paying for (TLC, ESPN, etc). We call the tech directly and he basically says there is nothing he can do. We then proceed to call customer service several times. They agree we should be getting the channels and state they will send "signals" and again, it should come through within the hour. Still, only grey screen.

We then called again and requested another technician come out last Saturday. However, someone with Comcast called us on Friday and stated they had identified the problem from their end, that they would just need to switch us from a digital signal to an HD signal, which hadn't been done presently. I had high hopes this would be the solution and agreed with them that they could cancel the tech coming out since they could fix it from their end. They stated that the channels should come through by Saturday at noon and they would call to check on us. Saturday passed, no channels, no call. A call AGAIN to customer service only netted us another more "signals" sent, and again, no channels. I am afraid we will be going around in this circle forever! I'm frustrated because I was looking forward to having Comcast service after a terrible experience with a competitor. Help!