Account in arrears while contract not signed

Some time in March, while on maternity leave, I got a call from a sales person from cell c selling a wifi-router. I had been looking for one but since I was home in the villages for the duration of my leave, I hadn't had time to shop around. So I listened to her, and she told me about a deal I couldn't refuse. We agreed that she would courier the router that she was promoting. She told me that she would call me in a few days time to check if I had received the package, and to finalise the contract. A few days later, the package arrived. I realised that it was some sort of indoor router, while I wanted a mifi-router. I immediately called Cell-c to inform them. They arranged for the courier company to come and fetch the package. The male sales person at time told me that I should wait for the call of the initial sales person to inform her that I did not like the package and have returned it, and reorder what I wanted. The call never came. And in August I got a statement from Cell C, the same came in September, and now in October. I just called the call center now, and the lady there says my "account" is in arrears. She cannot assist about me not knowing anything about the said account. And there is no one who can assist me today. I am so spitting mad right now. How do I owe Cell C when I never authorised a contract in the first place! How do I owe you when I returned your device! And now the call center lady says this is going to reflect negatively on my credit rating!!!