I am having the same issue. I received the email below with had a link to a "Learn More" page where I tried to add unlimited data for $30 more a monh but get the error message, "Temporarily unavailable
The product you’re interested in isn’t available for purchase at this time" and a URL of https://www.xfinity.com/error/buy/sorry?errorCode=DFPLN4000.
How do I sign up for unlimited data?
You’ve reached your Internet data plan threshold
You’ve used all of the 1.2 TB (1229 GB) of data included in your plan for October 2020.
We understand life happens and that overages occur from time to time. As a courtesy, we’ll waive this month’s overage fees. This is your last complimentary month for the next 12 months. Please be aware that if you use more than your 1.2 TB plan again, you’ll be charged $10, plus tax, for each 50 GB of data you use, up to a maximum of $100.
Welcome to the Xfinity Forum, @atlantadavida! We appreciate you letting us know you're running into the same issue others are when trying to add unlimited data to your account. I know this must be frustrating. I'd be happy to help get this taken care of. Can you send a private message? To send a private message, click on my name, "ComcastChe," and then click send a message. Please include your first and last name and address.