No credit card limit increase to foreign nationals

I have been trying to increase my credit card limit, and these applications have all been denied by FNB for no apparent reason. I last app**** recently, and I had to call to follow up, since there was no communication from FNB, only to find out it had been denied. I have been employed non-stop in SA for the last six years, have no debt etc etc. They will only allow a very low credit card max limit which I had for the past two years. This amount is not enough if an emergency were to happen, and I have proven for the last two years to be consistent and pay on time. I fear this is because I am a foreign national.