Whenever I try to add the $30 unlimited data option using my own modem, I get the error https://www.xfinity.com/error/buy/sorry?errorCode=DFPLN4000. I see many other threads reporting the same issue.
Hello @mirkendargen, thanks for reaching out to us on our Forums page. I do apologize that you're running into this, but this is a known issue we're working on correcting. In the meantime, we would love to assist you with getting Unlimited Data added to your account. Can you please send me a Private Message including your first and last name as it appears on the account?
To send me a Private Message, please click my name “ComcastAmira” and click “Send a message".