Terminating expired contract proving to be very difficult!!

<p>I have a top-up contract with Vodacom which expires end of this month, i was advised that should i not wish to continue i have to notify Vodacom one month before the last month of the contract, i did that then to my suprise after the notification the subsciption then increased on my contract, when i tried to call them (Cancellation contact centre) they hanged up on me. </p>