Absa credit card nonsense

I have a credit card and the limit is R2000, I used the whole amount. I pay the installment fee is paid every month on time. However I can use my credit card even though I never missed a payment. But I'm told that I can use the credit card when I make a payment of for example R15000, that is what will available for me to use. I really don't understand how Absa credit cards work because I thought that when you pay the monthly installment. You are then able to use the amount allocated on the credit card. I'm very annoyed and confused because it seems as if I took a loan instead of a credit card. This is utterly ridiculous