The most effective communication with opposing legal representatives is sometimes not to ask questions, but rather to tell them what the problem is.
For example, if the other party withholds the child's time with you, contact the other party first and propose a suitable solution, such as make-up time. If the other party is unwilling to negotiate, then contact the solicitor, stating what orders was breached on what date and what action you intend to take the rectify the problem, or what action you want them to take to ensure similar issues do not occur in future.
Remember, it costs a client money every time their legal representative receives correspondence, and it costs again when they send correspondence back, so since it's not you paying the solicitor to answer your questions, it's somewhat understandable that they may not respond to questions when you send them. This is why I suggest taking a 'don't ask, tell' approach, if that makes sense.