Vodacom is *****ing my airtime (Money).

I mistakenly clicked on the option to automatically load 10 megs of data for the cost of R3,00 per time. The telephone number +*** gives me the option of cancelling the service by sending an sms to *135*6# but when I do that a message comes back saying message not sent , messages cannot be sent. Vodacom is eating all my airtime up but not giving me the option to automatically cancel the service . I'v been to the Vodacom stores are there the staff informed me that they cant do anything about it. Now I don't need the service when I am at home because I have vodacom wifi , but it still buys date and finishes my airtime so when I try to make a call I am always out of airtime . Does any one experience the same problem, I am thinking about a class action suit against Vodacom for *****ing my money