Disappeared data

I bought 250mb and a few hours later I check the balance and see that I am only left with 90mb but I didn't use my phone either than whatsapp. I then decide to call the contact centre so they can check what happened to my data, I spoke to Precious Tseka who told me that I was on the internet I know what happened to my data I must tell her. Would someone who knows what they doing at Vodacom please advice why my data disappeared... I have ensured that all the apps which use data were off as well as background data is always off. My device auto updates are always off.