The technical answer to this is that if there is a provision in your court order for telephone contact between the children and their father, you may be in violation of that provision. Many court orders have provisions that say the children will have reasonable telephone contact, or contact for a specfic schedule. So, wihtout more information, it is difficult to give you the precise answer.
However, the children should be talking to thier dad. The issues between you and their dad are not issues they should be aware of. It is unfortunate that your son saw you cry and was aware of the conflict between you and his dad. It is always best if you can keep them insulated from that conflict.
The child support is also something the children should not be made aware of, and he should not stop paying just because he is mad at you or the children.
What you should do is encourage the children to talk to their dad. Encourage them to be truthful with him about how they don't like his angrey words. What you should not do is communicate to your kids, verbally or non-verbally that you dislike their dad, that you don't want them to talk to him, you just need to let them know you support their decision and effort to be honest.
You should also contact your local child support agency about the late child support.