Data disappearing into thin air

I took out a 10GB/10GB data contract in May this year. Every single month my data is finished ahead of time, so I also use a prepaid Telkom sim card for the rest of the month. IT IS VERY CLEAR THAT VODACOM'S DATA RUNS OUT MUCH FASTER THAT TELKOM'S! 2GB of Telkom's data will last almost a week, where 2GM Vodacom data will last maybe 3 days if I am lucky. This month was however a new record! It is the 3rd of the month and ALL of my 10GB is gone! This morning alone, I had about 700MB left. I only downloaded a few e-mails that can't be more than 50MB and now the 700MB is gone. After experiencing the same thing earlier in the year, I have switched of EVERYTHING possible to try and save data - the tiles on my Windows 10, my phone's update, Facebook Autoplay videos etc. etc. I LITERALLY CAN'T WAIT TO GET RID OF THIS CONTRACT, this is ridiculous and I have a very good benchmark in the form of my Telkom sim card to compare Vodacom with. WHERE IS ALL THIS DATA GOING? I WOULD LOVE TO KNOW!! It is clear from the complaints on the internet that I am not the only client asking this question!