Yes, contact Comcast with a rational, calm explanation of what happened, the truck number and a description of the driver if possible.
I do this when I can. Here's an example from last week...
My complaint:
This morning, 1/6/10, I was cycling to work northbound on the bike/pedestrian path that follows Alaskan Way at the downtown waterfront. As I was approaching the intersection of S. Jackson Street, a large Cedar Grove truck pulled entirely across the bike/pedestrian pathway on HIS red light (vehicles and bikes/ped had the green/walk right of way). As I approached the truck moved forward slightly and I feared the driver was going to continue on and make the turn oblivious to my approach (with lights on, a bright yellow jacket, white helmet, etc). I yelled at him to stop - a little angrily I'm sorry to say, but he was in a huge truck totally blocking my access to the intersection. The then yelled back at me saying something to the effect of, "I'm stopped what's the problem?" I ended up having to ride around the front of his truck, across the defunct streetcar tracks (a dangerous move on a bicycle) and manouver back onto the path.
The problem is the driver did not stop before the well-marked pedestrian crossing on his red light. He then saw me approaching and could not get out of the way. He then took his foot off the brake, allowing the truck to move slightly forward and then put on his brakes again when he couldn't make the right turn on red due to oncoming traffic (including me). He blocked the right of way off pedestrians and cyclists at a busy intersection (note the ferry dock is right there). I have never had a bad encounter with any of your drivers before. This one had a particularly bad attitude. He does not own the road.
Their response:
First I would like to apologize for your experience this morning with our truck. I can assure you that protecting the safety of our employees, customers, and those of the public is very important to us here at Cedar Grove. I spoke with the driver this morning and explained to him that he needs to be continuously on the look out for other vehicles, pedestrians, and especially cyclists. I stressed the importance of looking out for cyclist because of the fact that they share the roadways with vehicles and a large vehicle like ours can be a little unsettling to cyclists especially if it appears that they are not fully aware of what is going on around them. Once again, on behalf of Cedar Grove I would like to apologize for what took place this morning and I would like to thank you for contacting us, because of people like you it allows us to grow and get better as a company.