Data is disappearing ********!!

I don't understand how I can consume 600MB in just 1 and half days while I have unlimited wifi at home. Vodacom you are *****ing my data and it's not on. I always have to add more data every month which also disappears in seconds. This is theft and you are *****ing from your loyal customers. I have been monitoring the trend and I was overseas for a week and wasn't roaming. My data was loaded on Sunday and when I landed on Saturday there was data. This morning I only have 600MB? How is that even possible?