Still paying for cancelled credit card

On 03/12/2014 I went to Nedbank Pavilion and requested for the cancellation of my secondary credit card, which was not being used anyway. The assistant at the bank cancelled the card and destroyed it. The following day, i.e. 04/12/2014, I contacted the Card Division and spoke to Thabese. He confirmed cancellation of the card and assured me that I will not be charged monthly for the secondary card. However, to date (June 2015), I am still being billed monthly for a card that does not exist anymore. I sent e-mails to Nedbank, but have not received any response from them. They obviously are quite happy to continue charging me, their loyal client for many years, and refuse to acknowledge that they have erred, and that I should be granted a refund for all the months that I have paying for a card that is no longer in existence. Thank you.