You are correct. If it says Retail, it can be purchased.
The only thing I can think of to ask if did you get the modem activated?
I suggest you post in the Comcast Help Forums
Those Forums are provided to Comcast customers, and are a great resource for vendor specific issues. There are Forums for computer issues, email issues, security, internet, cable tv, CDV, billing, and customer service.
Many times we, the users there, can provide answers tech support and customer service can't.
Click the link below. The forum landing page will open. Click Sign In
. Log in with your Comcast user ID (the part before .net) and your password
. You will next see a first time forum users page, asking you to choose a screen name for use in the Forums. Once you set that up, you'll be taken back to the landing page. PLEASE DO NOT USE YOUR COMCAST EMAIL NAME FOR YOUR FORUM USER NAME
Before posting, take a moment to read the Posting Guidelines
. The link is on the top right hand side of the page.
Then choose the appropriate board to post in. In your case ask in Basic Internet Connectivity And Modem Help.
One thing to be aware of: By default you will be notified via email every time someone replies to a topic you have started or replied in. If you do not wish to receive the notifications you can disable them by clicking My Settings/Subscriptions & Bookmarks
the box next to Automatically subscribe me to topics I participate in
. Scroll down and click Save
DO NOT USE THE UNSUBSCRIBE LINK IN THE REPLY NOTIFICATION EMAIL. Due to a quirk with Lithium, the forum provider, if you use the link it severs the connection between your forum user name and the email address you sign in with.
Result: your forum account no longer exists in the database and it tells you that you are banned.
(Once you get to the forum, save the page to your favorites/bookmarks. If you want to get to it from the Comcast home page, you have to jump through hoops to reach it)