Account balance

I have a blue bean credit card with a balance of R13 000. Ive been paying an installment of R300 for over a year via debit order. I have been receiving statement every month but the balance remains the same. I have not used the card in two years yet the balance does not decrease. When I tried to speak to the agents at the call centre,they are just rude,impatient and no help at all. I had defaulted on my payment in January 2015 and when I was making arrangement I was too that I had to pay for a payment I skipped in September 2014. Now instead of catching up with one month's installment I have to deal with two.