You need to have a paper trial for everything that you served upon him. In family law, you can serve the other party with you responses and documents via first class mail or personal service. Since he is claiming that he never received them I would now resort to personal service and this must be accomplished by a non-party. You can have a friend or relative serve him but it might be better to pay a process server and they aren't that much. The party serving the documents must then complete a proof of service showing what documents were served, when and where they were served. This proof should be filed with the court. That way if there is a question regarding service, the judge is going to believe a registered process server.