Vodacom don't **** us please

Good day

Vodacom is not doing me write, I bought an I phone on contract and the contract ended last year. I went to the branch to cancel the contract as it was the end of our contract but they said i should call and cancel the contract then I did just that and the consultant bagged me not to cancel but Said no, now they are calling me saying am owing all those months whereas am no longer getting any of the benefit so my question is what service are they charging me for, they say the guy who was supposed to update on the system never updated that's why they still charging. My question is why and how so, I just regret doing business with such company Vodacom your service is the worse. my ***.