Acknowledging the mistake but not taking responsibility

I went to Vodacom Chatz Connect key West Shopping center some time last year to make an upgrade on a contract that was due. The salesman helping us was very helpful and we were happy with his service. What I didn't know was that he made a mistake and upgraded the wrong number that I was supposed to cancel not the actual contract number. I found out after the deducted amount was not the one agreed on, on the contract. I went back to check why was I paying more than I expected and the manager there a Mr Sanjit looked into the computer and said the only amount showing was the one agreed to. He advised me to phone vodacom. I called vodacom, that's when I learned about the mistake. I went back again to the store I found the same gentleman who was helping me with the upgrade. He saw his mistake and acknowledged that it was his mistake he upgraded the wrong number, he then asked that I come back when the manager is there as he is the one who can help rectify the situation. I went again found Mr Sanjit but he was not honest and helpful as he seemed like he wanted to make it look like i was the one in the wrong. He kept asking questions like I did wrong. Mind you when I entered the store the salesman went outside and I had to explain like I was in the wrong. Okay the salesman came back and explained the truth and he was honest about it. Mr Sanjit before told me to my face that the salesman didn't tell him anything. He promised to call vodacom to cancel the wrong contract and rectify the mistake and he will call me back but until now not. Vodacom is taking my money without even calling first. What do I need to do?