Vodacom - Cancel a data package

I have been trying to cancel a data package for months now. I am on a month to month contract now and I don't need the data anymore. Everytime I phone Vaodacom they tell me that I am this excellant customer and comes up with all these reasons and other deals, which I am not interested in. I am trying to save money. I dob'y need the data. The R 250.00 I am paying now I need for something else. The they tell me I need to give a months notice, and the reference number will only be generated and send to me once they have processed the cancellation, then I don't get anything becasue they dont process the cancellation. I can't phone from work or during office hours.
How can I get this cancelled ??