Impossible to contact

I am trying to cancel a credit card transaction for an internet transaction that was misrepresented. This morning I spent over 15 minutes on my cellphone trying to get hold of the Standard Bank credit card services, but to no avail. The line just rang and rang with the ubiquitous 'currently very busy' message being put out from time to time. I can't recall anytime when I have not heard that message. I need to know how I go about cancelling a credit card transaction. Mike King