Beware sneaky promos which catch the consumer out

In June I received Vodacom sms informing me that I was being given 300MB of promotional data.At the time I had R113.96 of airtime left.I utilised the data bundle but noticed that although I had made a few brief calls on my prepaid phone from 19 July when the balance was R102.46, my balance had decreased suddenly to R52.07 on 24 July. I didn't understand this-I had received an sms on 23 July saying that Vodacom hoped I enjoyed my free bundle followed by another promotional offer (there was nothing to indicate that once the promo data ceased that I would continue to be charged (usually you buy a separate sms or data bundle if you want to utilise them, which I didn't)).On 27 July I tried to call but couldn't so I requested my balance which came back as R0.I phoned Vodacom & was told it was depleted by the internet usage after the 23rd. Very sneakyof Vodacom!The sms on 23 July didn't warn me that should I continue to utilise the internet or leave my cell on to automatically update that I would be further charged and that it would come off my airtime balance which I assumed was for calls only. I would like my R100 back please as I feel I have been unfairly & unknowingly duped by Vodacom