Wow, I think its great that you were able to stand up for yourself and tell your mother and sister that their behavior is unacceptable to you.

I understand why you left without saying goodbye. Yes, in a perfect world you would have been able to discuss things with them at the time, but given that you were so mad to the point of yelling/punching a wall, I really do think you did the best thing by walking away.

I think that if they try to put you in the middle again, then you tell them that you are not going to put up with their behavior anymore. If they do not stop, then you walk away again, and hopefully you won't be as mad and will be able to say something like "this is unacceptable to me, I cannot be put in the middle anymore, and when you put me in the middle I am just going to walk away". It may take a number of times of repeating this, but after awhile your sister and mother will get the message that if they want you around, if they want you in their lives, then they will have to learn to respect your boundaries. Yes, this is indeed boundary setting. I think you are off to a good start so far. The important part of boundary setting is to enforce the consequences....i.e. "if you put me in the middle, I will walk away" and then make sure that you follow through by walking away (or leaving, etc.) when they step over the line. You can't control their behavior, but you can say what sort of behavior is acceptable to you, and then remove yourself from the situation when they are treating you poorly.

You have a right to your space, and you have a right to tell your sister that you need space without her guilting you. Really, if you don't want your sister to call you, then she needs to respect this, no matter what your reasoning is. Even if you had no reason, then she should still respect that you need space.