Vodacom contract

I was paying my cellphone contract from Vodacom. Once I finished paying the cellphones. I asked them to cancel all airtime which Vodacom was putting on a monthly basis. Still even today Iam failing. An agent called me to inform me that I can get data and minutes as part of the new contract and if Iam not happy with that one I can change it. I have call Vodacom numerous times to cancel any contract that I have with them but even today Iam still struggling. Everymonth they are adding Airtime or data or minutes, Then I call them again. According to Vodacom they cannot cancel. The contract must continue either they include the Airtime which Vodacom was previously giving before. I've never heard of such things. I urge people not to take a contract with Vodacom. They make excuses when a customer tells them to cancel.