Vodacom and loss of data.

Last Thursday our electricity was off and so I used my hotspot on my phone to load my mail. I have to stress that other than my mail I did not use the computer for anything else. In under 10 minutes I was notified that most of my data had been used - in fact 793MB to load 5MB of mail!! When I phoned Vodacom to say there had been a problem I was fobbed off like an idiot who knew nothing about how a computer works. First I was told that hotspot uses a lot of data - over the years I have used hotspot extensively and never had so much data disappear - in fact I don't know if it's possible to download that much data in 10 minutes on 3G as we don't have 4 G in our area. Then I was told that windows 10 was probably doing an update - I checked and this was not the case. The thing that really got to me was how the service people spoke down to me as if I didn't understand what was going on. What I certainly understand is that Vodacom somehow stole/lost my data and now won't take responsibility for it. I was also told I had made a whatsapp call and that whatsapp calls use a lot of data. This call was made after I had had 793MB of data disappear from my account!