Disappearing Airtime

I am on a top up contract which means I get airtime once a month and with that I can buy data and use the airtime as usual. My airtime always carries over from month to month which results in large amounts of airtime all the time and as a result I usually buy 1 gig data bundles as I need them. I haven't had to buy additional airtime in years and buy data as it runs out (Vodacom sends sms's saying that my data is nearly finished and that I have 250mb or 200mb etc remaining). So as I receive the sms I buy data. Today my phone stopped working and when I checked I had R0 and no data. Yet I haven't received a communication regarding my data for a long time. When I call them, they inform me that my data ran out on the 3rd of October, when I then purchased a power bundle which lasts for an hour (which I recall doing) and once that was done, I never purchased another bundle. My issue is that I didn't receive any other communication regarding my data being finished, as I usually do. So as a result they say that I have been charged out of bundle rates since the beginning of October.

I am highly annoyed. Vodacom's service has always been efficient and helpful. Yet now, over R1000 of airtime has been taken without any communication over the last month all for data.

This has happened to my brother multiple times without communication from Vodacom.

I don't understand how their communication is effective at times and not at others. If you have a system then it needs to work the same way for everyone. Very frustrating.