out of bundle shark excessive data billing

In August 2013 i purchased a R99.00 2gb Vodacom ****le special (No ***)at your blue route store in Cape Town. <br> All running and working properly until Feb 2015 whereupon i receive an account of R440.00 odd rand and another for R6900.00 totalling R7375.66. Alarm bells start ringing as this is not what i signed up for R99.00 a month all very odd on calling your call centre they say it is an \open line"contract which i am certain didn't agree to and what is even stranger is that the period Aug 2013 - Feb 2015 if the 2gb was utilised within the month period then it would be cut off and i either had to purchase more data or wait for the cycle to kick in again at the start of the new month"