Handed Over Unknown Arrears which had subscribed

From Last year till to date I have been receiving calls from Vodacom consultants and now their debt collectors for the account I explained I had no knowledge of and in any case which has subscribed. I haven't had a Vodacom Contract for the past 7 years. In that period no one from Vodacom ever communicated or sent letters to me until last year. I indicated to that person that I had no knowledge of any arrears with Vodacom as I last had a contract with them about 7 years ago. I could not even remember what was my phone number then. I also told them as I have had no communication with them the arrears/account had subscribed. I indicated my desire to defend the matter should it come before the court. Without them sending me any breakdown of my purported arrears, they have decided to hand my account over to debt collectors. I repeat I don't know about any arrears as a long time has passed. From my knowledge, the period over 7 years that I had no communication from them, rendered this account as subscribed. I am also prepared to defend these arrears for which I have no knowledge of. I also suspect they listed me on credit bureau which I believe is an injustice.