It is not necessary to say OK when you set the Flash to OFF.
When set to OFF it will stay that way.
However, if your turn the camera OFF the Flash setting will change back to ON.
That is the normal function.
If you are wanting the flash to be OFF after turning off/on the camera,
I don't think you can do that.
I suggest you contact Samsung service.
Or you can post your question on the Samsung Forum: