Error message when attempting to update payment method

I need to update my payment method and setup auto payment for my checking account but keep getting the same error message, "Looks like something went wrong." I tried the app, the website, and multiple devices and browsers. I have spent about 6 hours on the phone with Xfinity support over several days with no resolution. They walk me through the steps of clicking on manage billing or autopay but always get the same error message. They say someone will call me back but they don’t. I asked them to rebuild my online billing profile since it seems to be broken, but they don’t know what to do. I have had Comcast since 1999 and now need to change my payment method to a different bank. I was able to change all my other bill payments with other companies in minutes but not so with Comcast.