Contract ended, notice given...billing continued!

I had a 24 months contract with Vodacom which I took when I bought a laptop at Makro years ago. I took the contract in Germiston and by the time the contract ended I had relocated to Kwa-Zulu Natal. However, prior to the contract ending I called the call centre (call recorded) about 2 months before and informed them that I will not be continuing with the contract on a month to month basis and want it terminated. I was assured the contract will be closed but the agent clearly just cancelled the debit order (my bank can confirm the debit order was not terminated by me) and did not complete the process. I went by life as normal until I got a call from Burnard, Raaf & Associates(attorneys) telling me my account has been handed over. I denied paying and told them what happened. Now suddenly I'm harassed by Hammond Pole attorneys threatening and intimidating me. Well, I'm a small fish but will not be moved by your threats and will not pay for your own mistakes. Train your call centre consultants well. Surely the fact the debit order has been cancelled on your side makes you liable. You will not be getting a cent from me and I will fight tooth and nail before I allow you to bully me!