Vodacom late debits!!!

<p>Hi there i have a few contracts with Vodacom, i change my debit date every single month to the 25th but every month they debit me on the 3th or 5th! and everymoth i call them to change my debit date but there is no change! its a simple request and everytime i call they say its done but till today i havent been debited yet! please do assist</p>