If you know what the court date is, you should show up. You have not been properly served, however, if someone presents a proof of service, and orders are then made, it is complicated and expensive to set aside those orders.
When you show up, you can request that the matter be continued, and order the moving party to serve you.
Please note that this answer does not constitute legal advice, and should not be relied on, as each situation is fact specific, and it is not possible to evaluate a legal problem without a comprehensive consultation and review of all the facts and court pleadings filed in the case. This answer does not create an attorney-client relationship