Outstanding amount on 'credit card'

I app**** for a store card and was declined. On following it up I was told it is due to an outstanding amount on my woolworths credit card. I had one years ago, paid it up and closed it. I closed it more than 5yrs ago. I have since moved between properties twice already and they still expect me to provide them proof thereof, of which i can't find anywhere in my house. Now this is annoying me. I want them to clear my name on their system as this will affect my credit status. Please help