Look at the Automatic Temporary Restraining Orders listed on page two of the Summons you served on him. He is NOT allowed to unilaterally change your health insurance coverage without your agreement or a court order. First, point out to him he is in violation of the court orders, and that if he does not immediately put you back on his health plan, you will take him to court -- possibly for contempt of court. If he doesn't comply, consult with an attorney for an hour on how to proceed.
(Disclaimer: This information about California law and procedures is based on the limited facts provided by the person asking the question and is neither privileged nor confidential. It is not offered as advice to that person or any other reader and does not form an attorney-client relationship. Readers in other jurisdictions should be aware that California laws may differ from those of their state.).
Standard orders that are issued by the California Superior Court prevent the removal of a spouse from the insurance. Talk to your lawyer about filing a Motion for Contempt. If you don't have a lawyer, see the court facilitator about how to bring this information in front of the judge.
Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on as such. This answer is offered for informational purposes only. It is not offered as, and does not constitute, legal advice. Laws vary widely from state to state and even county by county. You should rely only on the advice given to you during a personal consultation by a local attorney who is thoroughly familiar with state laws, local rules and the area of practice in which your concern lies.