Once again Vodacom deducting money from my airtime for out of data bundles

Once again Vodacom is deducting money for out of data bundles from my airtime on the 23 and 24 July. I have no contract with Vodacom as I top up with airtime and internet data as and when I require. I have no subscriptions. Why does Vodacom deduct money from my Airtime? This is happening on a regular basis. Nothing but dishonesty from Vodacom.