Nedbank card division has committed ***** by claiming to have given me a credit limit which they did not .can i sue them for all the pain they are causing me ?

I had nedbank card some 8 yrs ago .the limit was 8000 and now nedbank is claiming my credit limit was 20 000 which is lie because they have more than trippled the interest of what I had initially borrowed to make my life miserable. They are cruel. They have listed me everywhere. I need help .I've always been paying .but today I owe them 39 000 from a 8000 card limit .how ? Please help me .I need help .is it even within the law for them to add so much interest