I find myself more in your friends position, of people not wanting to talk to me or not answering my calls, not that I talk that much about my own problems, maybe it might be a good exercise to reverse the positions and imagine what it might be like if your best friend was cutting you off and hanging up on you, then maybe, just maybe it would give you more patience and understanding of your friend, what if they have no one else to talk to, its one thing if your cutting of a friendship to someone who has lots of people to talk to, quite another thing to cut of ties to someone who might only have you as a friend.
I do have friends that constantly talk about their problems, so I talk about mine to them, other friends talk about their problems much less, I try to do the same to them.
So basically try putting yourself in their shoes, it may be that your friendship is not even so important to them and that's why they feel free to waste your time, and it might be quite the opposite, that you're the only person they've got. Think about it, meditate on it. And do what you think is right. That's the best you can do.
18 years ago I made one of the most important decisions of my life and entered a local Cambodian Buddhist Temple as a temple boy and, for only 3 weeks, an actual Therevada Buddhist monk. I am not a scholar, great meditator, or authority on Buddhism, but Buddhism is something I love from the Bottom of my heart. It has taught me sobriety, morality, peace, and very importantly that my suffering is optional, and doesn't have to run my life. I hope to give back what little I can to the Buddhist community, sincerely former monk Johnhttp://trickleupeconomictheory.blogspot.com/