How do you know if someone blocked your number?

I've been trying to talk to my best friend brandie ._. I'm not sure if she blocked my number or not, last Time I talked to her she seemed sorta mad at me...I'm not sure if she blocked my number or not, when i try to call her it goes straight to voicemail and when I text he it says message has been sent. How do I know if she blocked my number or if her phones just off?