extended payment arrangement

Regardless whether I use the computer or the myatt app, when I attempt to set up an extended payment arrangement from the page:  
https://www.att.com/my/#/makePayment/arrangeLatePayment
it will not allow the transaction to go through.

The error message I receive is:

"We are unable to process your transaction at this time. You may wish to confirm the information you entered and resubmit.(PMT1401)"

I have also tried to phone, but this option does not appear to exist when phoning.

Please advise.

Thanks,

Charley