Yes, you can sue to recover damages, although you may not be able to recover the business as that might require a mandatory injunction. You need to consult a business litigator who can advise you on the relief available to you, possibly a negative injunction prohibiting them from entering the premises and providing services to your customers. Gather together all the docs showing your ownership of the biz and stating what you told the employees. Then show them to the attorney.
DISCLAIMERâ€”This answer is for informational purposes only under the AVVO system, its terms and conditions. It is not intended as specific legal advice regarding your question. The answer could be different if all the facts were known. This answer does not establish an attorney client relationship. I am admitted only in California. (Bryant) Keith Martin sbbizlaw.com
This is clearly not right. You have a claim. However, to get the business back you need a Supreme Court suit with an Order to Show Cause. Will take thousands of dollars in legal fees. There is no other way to proceed.