It can be frustrating when you are having difficulty communicating with the mother of your kids. Here are some suggestions to address the situation and improve your communication:

1. Communicate openly: Have an honest conversation with her and express your concerns about the lack of communication. Calmly explain that it is important for both of you to have open and consistent communication for the sake of your kids.

2. Understand her perspective: Try to understand her reasons for not picking up your calls or responding promptly. Keep in mind that she may have her own commitments or personal challenges that are affecting her communication.

3. Establish boundaries and expectations: Discuss and establish clear expectations regarding communication. This could include agreeing on specific times or methods of communication that are convenient for both of you. Also, ensure that both parties understand the importance of prompt responses, especially in situations regarding your children's well-being.

4. Be patient and flexible: Recognize that everyone has different communication styles and schedules. Be patient and understanding if she doesn't respond immediately. However, also emphasize the importance of timely communication when it concerns your children.

5. Seek mediation if necessary: If your attempts to improve communication are not successful, consider involving a mediator, such as a mutual friend, family member, or professional mediator. Their role would be to facilitate a conversation between both of you and help find a solution that works for both parties.

6. Focus on positive co-parenting: Regardless of communication challenges, prioritize the best interests and well-being of your children. Show that you are willing to cooperate and work together even if communication is difficult, as this will foster a healthier co-parenting relationship.

Remember, effective communication is the cornerstone of any successful co-parenting relationship. By approaching the situation with patience, understanding, and open communication, you can work towards resolving this issue and establishing a more harmonious co-parenting dynamic for the benefit of your children.