Charged for Web Ad I did not authorise

I have been charged for a Web Ad on my Telkom business account for the last 2 months. I called Telkom informing them that I did not request a Web Ad and that it must be cancelled and my money refunded. The operators advised me that it will be done immediately. A month later I notice that the Web Ad then appears on my December invoice so it obviously was not cancelled. I call again and an operator then tells me that Telkom is unable to help me and that I must contact the Yellowpages. Why was I not told this the first time? The operators at Telkom have been most unhelpful, they chose to remain silent and even admitted that they have no way of helping me. What gives Yellowpages / Telkom the authority to debit my account for an ad that I did not request or authorise. This is theft! I have tried to call the Yellowpages as advised by Telkom and NONE of their telephone numbers work. They also do not return any of my emails. Since Telkom is billing me I think it is their full responsibility to cancel this ad and refund my money. I demand it!