Failing to cancel a lapsed contract despite numerous requests to do so and still being billed.

I've been trying to cancel my data contract with vodacom for the last 2 months and have also requested that I be refunded the amounts debited since I gave them notice. I had a marketer contact me today who informed me that there is still no notice linked to that account despite the fact that I have emailed them and called them on numerous occasions. I was even rudely informed the last time I phoned that if I did not receive a response from them, it's not their problem that it hasn't yet been cancelled.