No it isn't. It's a scam. I contacted Comcast as I have never had had an account with them and they have no record of it and told me to put a fraud alert up immediately
Its comcast or someone on their behalf .they can apparently change terms of their contracts wait untill you change service then they bill you for unknown charges . When they call press 0 # or* i pressed all three when you get somebody tell them you are a minor or its a childs phone and you will report then to cps or the local police for child harassment has worked so far .i have a friend who is good with computers so he will be looking up the office address .i will post this for everyone as soon as i get it so you can all go there in person and do whatever you fell you need to.