I cant change my resolution

When i am trying to change my resolution in settings, for example i have 1980x1080 screen and i am changing resolution to 640x480 from game settings but it changing itself to 1980x1080 again. And when i opening game sometimes its changing resolution to 640x480 randomly. But like i said, its random and its not happening when i am trying to change from settings. I was gonna crash out today because of that. Please fix it.