Expired Contract

My contract for my secondary phone number expired end of August. I called Vodacom, where they are always "experiencing high call volumes", and was advised that my last bill payment would be for August, and I would not be billed for September. I have made the August payment and then called the cancellations department. They logged the cancellation on the system (according to them), and to my surpise I was billed for September AFTER the contract ended in August. Is this not in breach of contract??? I called again on the 3rd September and I was advised that they have NOT logged the cancellation request. The lady that assisted me said she would then do it for me, and gave me a reference number ***, and that she would email the credit department to see if they can s**** the bill for September, as I have requested the cancellation previously. Sha also said that she would call me back on the same day, or the next, but it is 2 days later and NOTHING! You guys are so quick to bill people and take money from them. You guys are in breach of the contract and that is *******! I am not paying for September bill and I want my secondary phone number on prepaid IMMEDIATELY!