Upgrade to unlimited plan

I need to upgrade to an unlimited data plan. Yes I actually need the data, 1.2 TB is not enough. I will not be using Xfinity's hardware.
I have tried using the /buy/plan/checkout/XFINUDAT link provided in the support articles, it claims to be temporarily available, and has done so for an unreasonable length of time.

If this is not resolved in a timely matter I will be terminating my Xfinity plan.  

It is genuinely absurd that I am even having to make this post.