inflated credit card liability

absa refuses to investigate credit card ***** on my account, my credit card details were used to pay for services, not once was my credit card swiped for the transaction or me giving details to gth e3rd party, i have no idea how it happened but all i know is that absa refuses to investigate and holds me accountable for a transaction i did not authorise on my card and they have a very convinient excuse that it was 6years ago. who's fault is it that their systems dont work? who's fault is it thet their staff is ***********. i am so dissappointed