Sears Mastercard has owed me $655.49 since March of 2009. They wont refund me the money or do anything about it. What can I do?

Somebody paid my sears card off as a gift and didnt tell me. Well I paid it off that month too just because I happen to be cancelling it. I did cancel it in March, and now sears wont give me my money. They keep saying they will refer me to the refunds department and Ill get a letter 2 weeks later saying they cant refund it. They want proof that I paid it, I shouldnt have to show proof that I paid them in cash in the store. They give you a little slip the size of a post it note and it fades in a matter of minutes. Im tired of this, I need this money. Thank you for reading.