Vodacom overcharges for so called out of bundle data usage

Whilst at a business lunch on 22 Nov I received a message from Vodacom saying that I had run out of "in bundle" data. Within a minute of that message I received another message saying I had used R111 out of bundle data. Within another minute of that I received another message saying I had used R151 out of bundle data and within another minute or two of that it went up to R301. This was very alarming. I didn't understand how I could've used R301 of data without so much as touching my phone i.e. not downloading ANY emails , messages, going onto the internet etc. I then received yet another message from Vodacom confirming that I had used R601 of out of bundle data. I have absolutely no idea how this is actually possible as my data had been off for a considerable period and I had switched it on for probably less than 2 minutes to check if I had any messages. I did not at any point during these few minutes download emails or use any apps (other than WhatsApp) and yet I had used another R300 of out of bundle data. I sent my partner a Whatsapp at 15:00 to say I'm switching my data off and when I switched my data back on at 16:30 I received another message saying I had used over R900 of out of bundle data. All of this happened in a matter of 3 hours with my mobile data being switched off except for switching it on for a total of about 10min. I contacted Vodacom as soon as I got into my car at around 17:00 and explained to them what had happened. The lady explained that she needed to refer the call to a technical person and that they would get back to me within a week. It has been 3 weeks and I have not heard anything back from them. I've had to follow up with them now and after 3 weeks, they still have no explanation as to how I could've possibly racked up R795 of data usage in 3 hours which is something I haven't managed to do in the last 12 months. The messages I received and my statement also don't coincide. The last message I received confirmed that I had used more than R900 of out of bundle data and yet my statement reflects that I used R795 of out of bundle data. Vodacom still intends on debiting an amount of R2014.79 from my account this month without any explanation as to why...Terrible service!!