I have similar issue. My i9502 suddenly have sim card 1 locked. When I go to <Settings> <More> <Security> <Set up SIM card lock>, it is found SIM1 is locked.
I tried to tick and unlock it, but it says "0 attempts left" and as a result, I cannot unlock SIM Card 1.
Now, I can only use SIM Card 2 on my i9502.
I have tried to refresh the firmware and the result is the same, i.e. SIM 1 is still locked and cannot be used.
Any hint to solve it!!!
Million thanks in advance.