My internet has been out for a couple days. I've done all He troubleshooting, the lights on my modem are good. When I called in to Comcast the solution I was given is since I have a SB6121 that I own, don't lease, it needs to be replaced as Comcast Internet will not work with this modem. Is this actually true?
That is incorrect. Information on this can be found at http://forums.xfinity.com/t5/Basic-Internet-Connectivity-And/SB6121-6141-End-of-Life-Details/td-p/27...
Are you directly connected to the modem (as opposed to being wireless) when testing your connectivity?
I'm able to see your modem online and ping it with successful responses.
I will escalate this post to have someone assist you further.