I want to say this with compassion: I believe strongly that parents should be able to speak to their kids-- particularly young kids -- during the other parent's time.
I know you are hurt and angry, and that you think she should "suffer" the consequences of her decision, which includes losing time with her children. But I urge you to do what is in the best interest of your children-- which is to allow them to speak to their mother, even though it was not your choice to put them in this situation. This is already tough on them-- don't make it worse.
What kind of relationship do you want to have with the mother of your children going forward? What do you want to model for them? How would you answer them if they were old enough to ask, "Why didn't you let me talk to mommy when she called?"
Dig deep on this, and ask yourself why you made that choice--and whether you can choose a different path.
You can set a reasonable boundary-- once per day, perhaps, and even a time frame, so that you are not getting calls all the time, but I think it's very important that kids as young as yours have regular, if not daily, contact with both parents.
If my H did what you did (not responding to calls and texts asking me to speak to my child), I would probably have been just as upset.
