I didn't call my girlfriend's birthday, I just sent a message. She has been angry with me, refusing to answer the phone or return my messages. What should I do?

I believe that if I were you, I would do the same and even break up. She cares about you so much that when you are important to her, your short message makes her feel that you don't value this feeling. Of course, she will reflect so much. I think she is really disappointed and sad. You should explain to her, let her know that you love her and care about her, and sincerely apologize. Women need to be coaxed into buying a bunch of roses or a necklace as compensation.