1. Your employee is self dealing and obviously not to be trusted. Remove all their electronic and physical access to your facilities and follow your company procedures for termination.
2. You thought you were buying product from a reputable supplier. Now it is of unknown origin. You need to verify the authenticity of the raw materials, performing whatever quality checks are needed to ensure that your current stock is not defective, adulterated or counterfeit.
3. Contact your previous supplier or other suppliers to get a replacement source of the materials so that production is not disrupted. Also inquire if they do business with the "fake" company or another company at that address. If you find out the employee's supplier and their pricing, you should be able to find out the total amount skimmed from your company.
4. Have your lawyer File suit against the employee for your damages. Your damages would be the money that they made through the fictitous company or the money that you could have saved if the employee did their job lawfully.
5. COntact the police to see whether the activity is considered criminal. Since you actually received the products ordered, this may be treated by the police as a civil matter.