Data ******* again

I ran out of data on Sunday 12/11/2017. I then bought 250mb, which was depleted within minutes, I bought again two 30mb which were also depleted within seconds. So I turned off all applications that find on data and bought R500mb of data. To my surprise, this was also depleted in seconds and there was no application running in the background or active that uses data. Today: 14/11/2017. I bought 250mb and a further 100mb. Again my data was depleted within minutes. I really don't understand why data is so expensive and yet Vodacom doesn't seem bothered to ***** data like this.