Letter to confirm written off debt

I had a debt for a credit card with Nedbank. When I phoned them to inquire about this debt they tell me it is written off, sometimes they say it has prescribed, depending who you talk to from which department but all the time when I ask for a confirmation letter that shows that the debt is written off or prescribed I get told that they don't give out letters. They refuse to give me the letter to confirm the debt is written off or prescribed.