Credit card cancellation

I have been trying for over 2 months to get a credit card cancelled. Despite going into the bank and sitting with the consultant while she cancelled the card telephonically, it is still not cancelled and I got an SMS yesterday to advise minimum payment due for a card a don't have and a service I don't use. WHY is it so difficult to cancel this card - and please don't tell me to call the credit card call centre - no-one can help me.