Vodacom blacklisted me for no reason

vodacom had blacklisted me for no reason. My contract with them expired in March 2014, I have called them in the beginning of the month and told them that I do not want an upgrade further. 3 days later I decided to take an upgrade, when the handset was delivered and it was going to cost me more I decided to cancel it. I have never used the handset and they came and collected it within couple of days (less then 7) . Today, a year later I tried to apply for a data contract with Neotel and was told that I am blacklisted by vodacom. Can someone please help me? What can I do now?