CARTRACK A BUNCH OF *******

I sold my car which fitted with a cartrack unit, back in 2010/ 2011, i cancelled my account with them, last month 8years later i get a call saying i owe a company called Nibo about R800 as they bought my debt from car track, like what the hell is this in the whole 8years i have never heard anything, now i get threats from these people everyday on my phone. PEOPLE STAY AWAY FROM CARTRACK THEY ARE A BUNCH OF ******, NIBO OR WHO EVER THEY ARE ARE NOT GETTING A PENNY OUT OF ME!!!!!