just asking

My Service dog Harley and I were told to leave my Dr's visit today. He has been there before, allowed in my Dr visits and as recently as a month ago was in the office while a Dr. did a small cyst removal near my eye. No problems ever here. Today I was. told he is not allowed. Harley is an English Mastiff, 182 lbs and growing. Yes he is only 15 months old but he does what he has been trained to do. He helps me with my Mobility and Stability as he has been trained for by me the owner and user. He does his job. I arrived for the Dr. appt. at 2:27 for a 2;30 appt, was checked in, sat down with Harley. Harley just plopped on the floor like any mushy squishy face gentle giant does. 8 minutes later I was told my had to leave! I said to the person asking us to leave he was my service dog. My question now is what are my options and who do I talk to?