Hi I got an sms to say my mobile data contract has come to an end

Hi I got an sms to say my mobile data contract has come to an end. I went into Telkom Kolonnade and told them I was there to renew my contract. I chose my package and the contract was processed. The lady that helped me said I would need a new SIM card because it was a different package to the one I previously had. I asked her if the old contract is now closed and she said yes and that the only extra fee I would have to pay end of June would be the 99.00 for the sin activation. I asked her why I was paying this extra because the info in the deals booklet showed free SIM card and activation but she said it was because I was getting a new number. I got an invoice just over a week ago to say I owe 919.00, I was furious and went back into Telkom at the Kolonnade and was told the lady that had helped me had not cancelled the previous contract and I was being charged for both. She then cancelled the old contract but said I was still liable for payment for the old contract because I only came in just over a week ago. I told her I was now paying for a contract that should of been cancelled in the first place and a SIM card and activation fee that should of been free and for data that I am not even getting. I am going for legal advice but I want Telkom to reverse all these extra charges that I have been charged for. My contract should be a flat 399.00 a month. Account No. *** Invoice No. A*** Regards Chrissie Winter