Contract ended, but handed over because of incompetence?!

Hi, I tried phoning with no success, I have a very irksome situation, On the 20th of January, someome from tracker let me know that my contract is ending i think end of Jan or Feb, can't remember the exact date, then i told him that's fine he can let it expire as i do not even own that car anymore for over a year now. Then ouy of the blue norman bisset phones me saying i have been handed over for non payment, with a balance of some R400 and something?

I find this very low, it is effecting my credit score! How can you hand someone over without even letting me know that i might have an outstanding balance, but this account has ended, so how can it go on?!!!!