Contract extended against my request to cancel !!!

Requested cancellation of my contract at the end of the agreed 24 months. a pre notice of cancellation was given and three months later Vodacom still forces me into a contract that I did not agree on by allocating me airtime I don't want and debiting my account. After calling the call centre , operators drops the phone on me and doesn't bother to call back and conclude the call. The operator still tells me I need to give another notice of cancellation , how is that possible? Why must I continue to pay for your own systems and processes in competencies??? You continued to debit my account without my permission and still want me to pay for that ??? How Pathetic !! I will move my contract to a place I am more appreciated .