Can’t change payment method

Help! I have tried on the phone with Comcast for over 2 hours, have tried online, and on the app and am very frustrated! I tried changing my payment info from the bank to a credit card and was hit repeatedly with the message that the system was unable to make the change and to try another method. I turned off auto pay even and tried and still no. I called my bank even and they said all is good on my end. This is my last resort. How can I change my payment method. I refuse to do another 2 hour call after having to be on a call earlier with them for 2 hours and on Wednesday for 2 1/2 hours! Thank you!