Vodacom's dishonesty

Vodacom called me last year in october to offer me 70gig for R307, I was advised that I was going to be charged a once off fee of R159 to put in effect and from the end of the month and that never happened. I was still charged the same amount and last month they charged me R423.98, at this point I'm considering cancelling my contract because this is nonsense. I don't have the time to spend hours on the phone sorting out Vodacom's problem.