Insurance policies of all types are regulated at the state level. Even people who are trying to sign up for the CA through the federal marketplace are referred back to individual states for the actual underwriting process. In each state, there is a Department of Insurance, sometimes called the Insurance Commissioner or something similar, and that department regulates, licenses and inspects insurance companies in that state.
There are several ways to find out the address and phone number for your state Department of Insurance. Your local Chamber of Commerce would have the info, and so would the state or county licensing offices, including both commercial and driver licenses. You also have the option of contacting any insurance company and asking them how to contact the Department of Insurance. If you have a specific insurance agent, she would have the information available by request.
Online, you can find the information from a couple of resources. The National Association of Insurance Commissioners, NAIC, is a conglomerate of the state insurance departments, and provides you with a clickable map that contains the current data for any state or United States province. You could also enter a simple search for your state and the department of insurance, and your favorite search engine can deliver the information to you.
The Department of Insurance is the consumer's protection agency. If you are unable to resolve a problem with your insurer, this is the place to turn. Similarly, you can contact the department with questions about insurance requirements, what companies are licensed, and any other details you need about an insurance company or policy written in the state. They cannot give you immediate information about a specific policy, but they can tell you what the regulations of the state require.