A VERY BAD SERVICE EVER

I had an account and have settled the account but unfortunately I overpaid them. I was told that I will have to simply go to any MRP shop and claim my credit but I was told that I cannot get it when I reached the Mr Price at Ngebs. I always get monthly statements now the money is going down bit by bit. I really dont understand bcz I dont owe them why do I have to pay for something I dont know. I told the client service that I want to close it.