MTN Bullies

I app**** for a contract online with MTN, I was given a phone that was faulty to say the least and I took it back within 7 days. After hearing nothing from MTN regarding the satus of my phone i decided to give them a call. The agent told me that MTN was changing their system so as a result they would not be able to assist me, i wouldn't be getting my phone and so I needed to cancel my contract and go apply for a new one at one of their stores. I asked her to initiate the cancellation, do she did. I then received communication from MTN saying I need to pay R5839. I've never used this contract, i still do not have a phone but I'm expected to pay this money???? Are you guys allowed to rob people like this? I've reached out to your customer service department with no joy. Can someone tell me who I can take this matter up with, because I refuse to be ****** by MTN