Vodacom 2 year contract don't mean 2 years

My wife Marsha Adams took out a 2 year vodacom cellphone contract at Game Promenade and after the 2 years was finish she got a call where she was ask if she wanted to continue. She rep**** no and ask that it must be stop which the person rep**** I will do it.After more than 4 months being debitted for this my wife reverse the payments and last week went to vodacom store in Zewenwaght Mall to sort this out. She got the shocking news that the account is in areas and paid the amount wich was over R1000 and ask them to contact their accounts department to cancel this. The answer she got was that she must contact them herself from a vodacom sim which she don't have and on the question regarding that she only sign a two year contract which should stop after 2 years no answer. My question is why do we sign a 2 year contract and it doesn't stop after the 2 years and why can we pay our account at the stores but they cannot sort out our issues.