Stealing my business

 Hello,

         My Question is about my business ID. I purchased a building with a friend 3 years ago. I recently discovered That he has put my business phone # on his business invoices (without permission) and has been receiving phone calls through my # according to my staff for better that a year (I was unaware of this till just recently). I recently witnessed him identify himself as the new owner of my business also telling the customer (while handing her one of my business cards) that these were old business cards but the address was correct. I told him to take my # off his invoices and stop telling customers he was the new owner of my business. I cannot throw him off the property because he is half owner of the property. He is attempting to get a license for business in the same building for the same type of business. What steps could I take since it is now very apparent of his intentions and where and whom my walking customer base is disappearing too. He also bullies my employees when I am not there.