My friend didn't call me back yesterday, is this a good excuse she made (please read first)?

My two weeks hasn't been calling me back latley. I know we have busy lives but I at least make time to call them so that shoes I'm a true friend unlike them! I called them both yesterday and no answer. One of them texted me back and said she is sorry that she didn't get a chance to call me and she'll be busy tomorrow but will call me when she gets a chance to. I said ok but five minutes later I called her again STILL no answer. I dont think that's a good excuse at all. Not good enough. I know I don't call everyday but I make the ecfore. I'm just going to end the frendship and stop talking to them.
I know she has her full time job (nurse) and she has children and married but that's no excuse.