Robed for MTN contract.

Their consultant robed me by letting me sign for a wrong MTN contract. She convinced me to upgrade with a 50 G data @ R100 MTN contract saying they were running a special. I did not intend to upgrade my contract since I had installed a WIFI at home and did not have enough money to pay for both. She insisted and offered me 50G @ R100, I got surprised when R200 was deducted and when I called and lodged a complaint, the company said they couldn't find anything wrong from the recorded conversation. I am quite sure of what I have agreed for but they refused to play the record for me. I am currently stuck with a R200 contract for 36 months and I am afraid I may fail to pay on some months. I want to cancel the contract or be given anything at R100 per month.