First you have a lawyer write the letter and perhaps it will have more impact.
After that, depending on your budget, you may wish to contact the Secretary of State or think about a civil action. I hope you never get to the last step, and it should not be necessary.
The above is general legal and business analysis. It is not "legal advice" but analysis, and different lawyers may analyse this matter differently, especially if there are additional facts not reflected in the question. I am not your attorney until retained by a written retainer agreement signed by both of us. I am only licensed in California. See also avvo.com terms and conditions item 9, incorporated as if it was reprinted here.
You can sue for misappropriation, unfair business practices, etc. Talk to an attorney.
This is not a comprehensive answer and it is impossible to provide a meaningful response without a consultation. Call us for more information. 619.797.5456 www.mataelelaw.com