Hello @srich2417, thanks for reaching out to us on our Forums page. We appreciate you being a Comcast customer with us. I am sorry to hear about the error you're running into when trying to add Unlimited Data to your account. We can definitely further look into this on our end and we would be more than happy to assist you with getting it added to your account as well.
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".