No FNB Credit Card for Permanent Residents

We are Americans who retired here 15 years ago and have enjoyed living in this country. We have had a Discovery credit card for most all that time with no problems at all. With the issues at Discovery Bank , I made application to FNB for their credit card at the end of July sending all my details and financial data. I received an email from them telling me there was a missing document , "proof of income." I had sent them proof of our income, but apparently they refuse to accept it because it's from the USA. My wife and I own our 3 bedroom home (fully paid for), our car, etc., so that we have no debts in South Africa or in the US. Our pensions are sufficient for us to live very comfortably here in a secure estate in Somerset West. I explained all this to them in a followup email 2 weeks ago and they didn't even reply. I even suggested that a card with R 10,000 limit or less would be fine. They still have not agree to issue me any level of card.