contract cancelled

I TOOK A CONTACT WITH VODACOM WHICH ENDED IN NOVERMBER 2014 ,BUT I CALLED THE CONTACT CENTER ON THE 01/12/2014 AND I SPOKE TO NONHLANHLA WHO TOLD ME THAT MY CONTACT WILL BE CANCELLED AND AS FROM JANUARY 2015 THEY WILL NOT DEBIT MY ACCOUNT.BUT TO MY SUPRISE VODACOM DEBITED MY ACCOUNT IN JANUARY 2015 SO I HAD TO REVERSE THE FUNDS BACK TO MY ACCOUNT.SO NOW THEY ARE TELLING ME THAT I OWE THEM AND THEY WILL HAND HE OVER FOR MY NAME TO BE BLACKLISTED .WOW WHAT A BAD SERVICE IM SO DISAPPOINTED .