Rude and not helpfull at all!!

I went to Hartbee****rt MTN to add a data contract to my existing contract. I gave the woman my cell number and with that details she drew up a contract and made me sign it. The next month it went of my sons account. Back to branch and they changed it from my sons account to my account and charged me R150.00. The next month I went back and was told I had to pay because it was a sim swop, told the woman that she made the mistake and she said, MTN does not refund customers. I don't know my MTN account number and worked in the telephone number on the contract when I signed for the deal. The woman has now left and all they say is that I signed for it. How can people working with public just be allowed to make mistakes like this and it just becomes the client's problem. And for the rest of the staff, I have no respect for them as they treat you like ****!! If you cannot rely on people to do a job right the first time how can you trust anybody!!