Dear Ex:
Pursuant to my attorneys' advice I am sending this letter to inform you that the children will not be at the police department on Friday, July 4, 2008 for visitation. My attorneys have advised me that since the children were not returned to me on Sunday, June ___, 2008 that all visitation should cease until a court hearing can be scheduled. You should receive notice of this hearing in the near future.
Also, my attorneys have advised me that all further communication should be addressed by email. My email address is xxxxxxxxx. This email account is solely and exclusively for communication regarding visitation. Please do not use this email account to communication regarding any other subject.
I think this should be it. Do not tell him you know when the hearing is, wait for him to be served to find out. Also, he never got the first letter. You bringing that up may make the judge ask what happened at the police dept. and that doesn't need to be dredged up again. You also should not dictate when modifications should be made and why give him the opportunity to do so. This is not legal advice, only my personal opinion. I do not practice family law. (my disclaimer)