Contract cancelling

I had a contract 7 years ago. After 2 years they still billed me for 8 more months. I did not upgrade so i had no new phone nor received airtime. I called customer care who told me I had to cancel the contract in writing as contracts don't get cancelled automatically after 2 years. I faxed them a letter and the required documents. 4 months later i found that they were still deducting from my account. I instructed the bank to stop the debit order. Last year, after 6 years a debt collection agency phoned me to tell me that I owed Cell c money. I had to pay for the rest of the contract for which i didn't ask nor received anything.They want to blacklist me but there is no way i am going to pay them. Could not even come in contact with their legal department