Having difficulty paying bill online

I keep trying to pay my Xfinity bill online and the bill pay keeps closing saying there is a problem and to check back later. I've tried Firefox and Chrome. I've tried using the menu at the left and the menu at the center of the page.  I tried the AI Chat (useless).

This happens more months than not.  As soon as I can, I have to get rid of Xfinity.  It is too stressful each month to go through this.