Need to add a Second Separate Line / Account to Single Address

I've never had more trouble getting a straight answer from a company than with Xfinity. This is legit the most ridiculous thing I've ever had to deal with to get internet. 

All I want is to add a SECOND account with a SEPARATE line to the same address. Which according to the Xfinity website is completely doable (See picture). I've talked to like 5 different chat agents, 1 of which almost got me through it, but wouldn't answer my pricing question. The others said it was not possible. Which makes no sense since it literally is an option on the website.

ALL I need is a new xfinity account, with its own plan, with a NEW line run from the street to the house where I need it. I do not want or need your modem (I have my own, which is better), and I have my own firewall (Unifi FTW). Please dear god someone help me.