SASSA ignores affidavits and ask me to prove a negative.

I app**** for an old-age grant since I am in my sixties. About 8 years ago I had a house that I sold then. I have not worked for any government institution for at least 30+ years. Despite me making affidavits to this effect, they would not believe me and kept on asking for a) My current house rates bill (which doesn't exist!), and b) My proof that I do not work for the government. (I do not- but how do I prove a negative???) SO THEY REFUSE TO GIVE ME A PENSION!