Billed for the phone I do not have

I purchased a contract phone at the above mentioned shop. In less 6 days it was freezing and the battery could not fully charge. So i went back asked them to cancel the contract as i was not happy and Maria shouted at me and my boyfriend. She said i should call customer care to cancel but they send me back to the store. I went on Vodacom customer care on line to report this, they said they will get back to me its been weeks of waiting for the respond. what hurts me the most is that the store manager call me stupid and I am billed for a phone I do not have the past 2 months. Please help me out of this situation.