I Want To Change My Payment Due Date

I want to change my payment DUE date to the first week of the month, preferrably to the 1st day of every month! Because AT&T changed my payment DUE date to the 27th and there is NO money in my account until the 1st of every month, so I am incuring LATE charges.  PLEASE change my payment DUE date to the 1st of every month.  I have called in a few times and yesterday was the last time and the representative said she could not help me and she would email me directions on how to do this myself online!  I have received NO email!