Paying for a contract without a sim card...

I have accepted a new contract with Vodacom telephonically in 2016. It was sold to me as an "ad-hoc package" for more data on my existing cellphone contract. I already have 2 other data contracts with devices with Vodacom and would not have accepted the new contract if it was sold to me correctly. I only discovered that it was a seperate contract when I did an upgrade on my phone. I informed the Vodacom Tzaneen branch that I never even received a sim card but was billed for it for more than 6 months. They never came back to me... I have phoned a few times without any luck. But, every time Vodacom phoned me to sell me something else, I brought my problem under the attention of the sales person, only to be told that they can't help me as it is not their department. I don't want or need the contract, but I have been paying it for a year (without any sim card/benefit). They would probably never refund me for my loss, but I don't know who to ask for help anymore. I will not go back to the useless Tzaneen Mall Vodacom again - as the call centre always tell me.