How can I change the due date of my ATT/Directv payments?

I now receive social security on the third Wednesday of the month.  My Directv due date is the fourth.  I called Directv to see if I can change it and she put me on hold.  When she came back she told me that I could not change my date.  I asked if it was the company policy, why was I put on hold?  What was she checking?  She said that if my account was ATT, it could be changed ,but since I'm Directv, it cannot.  I was then told that there would be a transitioning from the two billing systems into one, but she didn't know when mine would be.  This last month I had to borrow the money from my neighbor and pay her back when my SS direct deposit came in.  I can't keep doing that!  Is there any way this can be done?  It doesn't seem right that as a long time Directv subscriber I shouldn't be able to do the things that the ATT customers can do now that it is one company.  Can anyone help me???