Change from top up deal to open line without consent

When i was due for an upgrade received a call from marketing people, since i had a contract with telkom thought i was dealing with telkom only found out its their agent when i stated having issues with the the topping up my phone, when i signed up for a new contract i was never told it will change to open line, since my previous contract was a top up, only to my surprise send emails to telkom since February being sent from pillar to post then i decided to call telkom and i was told i would be charged R400 to change back to top up deal, which i feel it's not my problem that the person who was assisting me decided to give me an open line without clearing it with me