Bad service by Ismart

I bought a cellphone on contract and in one year the phone got a problem of charging. I smart sent me a new handset, and I was happy with their service. Within few months I lost my contract simcard. I reported the matter to I smart. I was told to pay a R150 fee for new simcard to be activated. The company sent me a new simcard but it had never worked. I was sent from pillar to post. Told that the problem is not with I smart but with the network. I was told to wait for four months. Four months came and gone. I was told to wait four another four months as their consultants kept telling me that the complaint ahs been escalated. I then decided let me stop paying for something I don't use after a year. Then they sent my name to debt collectors threatening to take my name to credit beauru. Until today, I am still paying for something that I don't use, with no benefits. I don't know where to complain about this company.