closed account but im still paying

I made my last payment for R100 and I received my statement stating I now have R4000 to buy and R100 in credit. I went to Edgar's and the lady at the counter confirmed this. I then went to get a few Items to buy on credit to my surprise the account is closed. Now I want to know why did I get a statement stating I have credit if my account is closed and why did you allow me to pay a closed account and lastly when am I going to get my R100 back.