Being misled by Vodacom notifications - data usage

The moment I receive sms's to say that I ran out of data, I IMMEDIATELY buy another bundle. Middle of January I noticed that my bill so far was R 2500. I contacted Vodacom and they said it is due to high data usage. Not even a week later, my bill was R 4288! That is roughly R 1800 within one week?! Could Vodacom not have 'warned' me earlier of irregular activity or so, as my highest bills are about R 1300. That is about R 3000 more than usual! I feel being misled by Vodacom's sms notifications and I think that this is ''easy money'' for them to make a fortune! I am due for an upgrade but I am not even sure if I want to stay with them as this is just unacceptable! I feel exploited! I also have another contract with them and I received a sms to say I have 3GB left on a data bundle. On closer inspection after realizing that I cannot rely on their notifications, I see that this bundle has been depleted. That is more than a week ago and I still have not received ANY NOTIFICATION to inform me. VODACOM'S NOTIFICATIONS ARE UNRELIALBE AND MISLEADING! CAUSING THEM TO MAKE BUCKETS FULL OF MONEY! AND THEY SMILE ALL THE WAY! Should Vodacom have warned me, I would not have received such a bill!