Contract cancelation

My contract is expiring next month on the 24th, I was told that I should call in to cancel but the phone rings the hole time without getting to an agent. I had a bad cancelation previously which vodacom was very *********** and I had to pay for their mistakes. Please assist me as I'm avoiding the same thing happening again which this is my last contract with vodacom I don't want anything thing to do with them ever again in my life now that I'm finally done with them I'm battling to cancel. Please help