Unfair blacklisting

I had a contract with them and ended it in 2016 and the account was paid in full. Apparently this yr 2019 i got a call from the attorneys saying my account has been handed over to them for non payment and i have an outstanding balance of R16000 i was suprised and went to the shop where i purchased the tablet nd it has closed down i went to another branch they said i must call vodacom account department. When i called them they said yes m blacklisted bt if i want more details i must call the attorneys. What confusing is that i have never got any statement via email or post or any telephone call encouraging me to pay then boom after 2 yrs i am blacklisted