Rain billing

I don't know what to do I asked your call center for help but i can't get through to billing my salary date has been charged to the last day of the month so i just wnated to ask for a billing extension as I can't change my date as yet I just wanted to extend it until the 30th because I'm getting my salary on the 30th of this month but rain don't understand I get my salary every month on the 15 but this morning we were told they changed it and I can't do anything so now I don't know what to do