query about closed account

I have closed my account with markhams in 2013. I told the sales lady who was the cashier after paying R750 balance to closed it. She said okay Sister it will be closed closed. After few months I got a call telling me that I owe 61 rand and I told them that how can I owe that money whereas the lady told me that it was closed. Now I got a letter saying that they going to garnish my salary. They don't have a right to do that because their staff is *********** they always in a rush, they don't help customers to their satisfaction. I am so so bored and don't want anything to do with them and I have send them an email cause I got furious with what they say that I have mentioned. Please help in sorting it out and clear my name.