Call the General Manager of the dealership and complain. Don't use foul language, but make your point with facts. Ask him if he would take his car back to his dealership knowing what you just told him. Also, ask him if he would recommend his dealership to others. Tell him you feel that your expensive fluid was stolen and you want it back as well as the hard earned money you spent on labor.
You will probably get a call from the service manager after that.