Vodacom can **** you big time. They renew your contract without your knowledge

Vodacom has changed my contract without my knowledge. I explained it to them last month.we agreed on cancelling contract and keep the number as prepaid but with fees. I couldn't afford it. They also didn't allocate me air time for October. Now they blocked my number and the lady from Vodacom called me to make an arrangement, of which I did. Then she said they will only unlock my number after the payment but couldn't answer why do they bill me for the service they didn't render.as they didn't allocate me airtime for October.The lady became irritated and tell me to pay either half of full amount before reconnection and then hanged up on me. I had a contract with Vodacom since 2000. They can't explain to me why my contract was renewed before time without thorough explanation. No one want to answer that hence the decision to cancel the contract. Now I can't make calls.