Criteria for adding a 5th line to Xfinity Mobile

I am a 25+ year Comcast internet and cable customer and have been with Xfinity Mobile since September 2019.  During this entire time, I have never had even a single late payment.  I have a credit score of 835 that has never been less than 825.   I have a family of 5 and have slowly been moving lines to XM as the lines came off of contract at Verizon.  Of the 4 lines I have currently on XM, only 2 lines are on phone payment plans, the others were paid in full.  I am trying to bring over the last line as a BYOD and I am being denied despite advertisements that state you can have up to 5 lines.

I've called support multiple times to understand why I'm being denied and never get a better explanation than "the system says you are at your limit of lines."  This answer is not acceptable to me as I believe they would be hard pressed to find a customer with a better credit score and payment history.  

The idea that nobody can give me a rational explanation for why I'm being denied is beyond frustrating.  The fact that I can't get anyone there to escalate the issue to someone with 1/2 a brain and capable of rational thought is infuriating   

If I can't add this 5th line soon, I will gladly pay off my two devices and head right back over to Verizon.