Purchased own modem

I only have business class internet and purchased my own modem in accordance to http://mydeviceinfo.comcast.net/ .  I purchased the Cisco DPC3008  The lady told me that she couldn't hook it up as they only allow customers to purchase Motorola's.  That Comcast page has several different models listed for the package I have.  

I brought that up to her, and she said maybe the page had not been updated.  (I highly doubt that, as the page is dynamic and was last updated a month ago).  

What do I need to do to activate my own equipment and get rid of this rental charge?