i regret taking a cellphone contract with cell c

I received a call from cell c agents informing me that I was due for upgrade so I went ahead and upgraded my phone, after a month of upgrading I received a letter from cell c informing me that I owe them R9944o03. And I should pay before 7 days otherwise legal actions will be taken against me, when I enquired I was told I now have 2 more lines that were opened in durban and am liable for the payment that I don't know all I want is for cell c to clear my name from all this madness and send me a clearance letter