Friends?

So I have this friend. I call this person a couple times a week to see if they want to hang out, get lunch, see a movie, or just talk. The strange thing is this friend never picks up, then when I do see this friend they say they never even got my phone call. I find this frustrating, very frustrating. So frustrating in fact that I no longer bother leaving a message (why leave one if they say they never get it).
Before anyone says anything, yes I have confirmed the number I have as this persons.
So anyone have any idea how to go about this? I’m just frustrated.