Credit card randomly stopped working

Hi I have had my credit card account for quite a long time and yesterday it stopped working in that every transaction which I attempted to use it on said that the card declined. I have made sure that there is sufficient money in the account and yet it does not work. The issue is that it randomly stopped working after it worked for a transaction at the gautrain station. I am now unable to use any card facilities as none of my cards work. <br> <br> I would appreciate your soonest response. <br>