Cancelation of contract

I have a contract with vodacom that expires this month, yesterday the 31st March I phoned them to cancel as it's a one of the conditions that you call to cancel at the end of the contract, I was advised that they can't load the cancelation because it's a month before the end of the contract. I was advised that I have to call on the 1st April so that it doesn't load a payment for May. I called today more than 5 times. I stayed on the line for more than 10 mins each call till it drops by itself. It's not a first time I experience this especially when you want to cancel you experience the non availability from them. When umyou require a different service u get help but not cancelation. I think because they want to force people to continue with the contract and blame you that failed to call to cancel and now it's a running contract again. I used these numbers to call them *** and ***