Vodacom is ****ming people

Last year I took out a contract of two iPhones for 950 a month without insurance. First months debit order there was no problem until I took out insurance for one of the phones only, the agent explained to me that they would only start debiting for the insurance the following month. For the past 2 months my debit orders has been sent back because of insufficient funds yet the required amount was on my account. Now I come to learn of an additional amount which I which is called pro rata something that I was not informed of when I took out the insurance and on-top of that I have to pay for the insufficient funds as well. Vodacom is the worst I regret taking out these contracts, when I call in they give me the run around.