Advice on this friendship, please!

Okay, so I have this supposed to be (best friend) of mine. We met in college and have been close going on 3 years. Now it's like she ignores me but not when "SHE" needs something or a shoulder to lean on when she's sad or upset about something. I text, call and have left her voice mails (no reply) few days later she'll text me and say something like (she didn't get my message or that she was feeling bad). I have been doing everything that a best friend should do and be like to her! I have done helped her out I mean I have done gone above and beyond for her, but she doesn't even be there for me smh. I don't let alot of people in my life because they just take advantage of my kindness. My question is what should I do? ? Do I let her go? Do I not response to her messages? Do I move on from this friendship? Like I don't want be a bad friend to her at all but these past few months that's what she has been to me. So please help me out on this.?