Got let go today because I’m not smiling enough

I'm a quiet person normally but Apparently even though I push myself to be friendly and communicate everything I do and ask if others need help and smile and etc etc. I'm just not smiling enough. ” I just need to do better, I just need to be more consistent, I just need to meet their core values” no one could tell me what I was doing wrong or how I could fix it. Just I need to be better