contract expiry

I just found out recently that I still owe vodacom about R500 , the interesting part is that I don't even know how possible this is because my contract with Vodacom expired more than a year ago. This happened when I checked my itc and was told I owe Vodacom .The excuse I got was that I never told them I didn't want my contract to be renewed of which I did on month 20 of my contract in a branch at Gandhi squre ,, I found this ridiculous and demand Vodacom to sort this unacceptable behaviour otherwise I will be engaging my lawyers.<br> NO one even had a decency to contact me .Vodacom need to stop messing around with people