Debit order date still not changed after request

On the 2nd of September I contacted the Vodacom customer care contact center to change my debit order date from the 25th to the last day of the month... I was advised by the agent I had spoken to that it would take affect immediately as it was done within 7 days before my actually debit order date... To my surprise this is not the case as Vodacom debited on the 25/26th of this month... I want to change the debit order date to the last date of the month thanks... Please ensure that I am not contacted by Vodacom especially Verculine... Please just change the date as requested on the 2nd of September.... Thanks...