Cancellation problems

I have been trying for the past 6 months to cancel a data line. On 9 January i went to Vodaworld in Midrand where a lady helped me to phone the cancellations department. I talked to a lady there and she could not immediately cancel the line but promised to phone me within a day to give a reference number and the confirmation that it has been cancelled. Up to date no word and the line is still active and I am paying for something that I don't want or need.