Why must I pay for an insurance that I cancelled?

Why must I pay for the contract that I cancelled? On the 4th of July I received a called from Vodacom insurance department they offered me a comprehensive cover for R200 for each phone and that would be R400 for two phones. I asked that sales lady a number of times if I would only be required to pay R400 she said yes. She didn’t say anything about pro-rata she just said I will have to pay R400. Now they want me to pay a lot of money. I called them and told them to cancel the insurance twice and I told them that I will not be paying for the insurance because I was misled but still they want me to pay so now my debit order for the contract didn’t go through because of the insurance that I have cancelled.