Handed over to debt collectors

I keep being harrased by debtsource about money I owe to ADT which is not the case. I gave 1 month notice when I cancelled my account in Jan 2014 And had to do numerous follow ups after the cancelation to ensure that my contract was cancelled. I was told that all money's that I was charged after Jan 2014 had been reversed and that I owd nothing and the radio was also collected from me. I have all the emails as proof. At the end of last year (2 years later) I was contacted by the debtcollectors and they said that they would blacklist me. I handed over all the documentation to Ayanda Moleka at Debtsource and am still being harrased till today about the account. Please sort out my account and get Debtsource to stop phoning and sending sms and emails to me as I owe you nothing. Your accounts department, is to say the least, useless.