"Unprofessional staff"

I would like to share my experience in Whipps Cross hospital yesterday I have a 4 years old son we went to the children outpatient clinic I had an list from my GP it says ' for children under the age 10 you do not need to book an appointment on Tuesdays and Thursdays from 09:30-3:30 just walk in to the outpatient clinic. I have contacted the hospital to be sure that I don't need an appointment and they confirmed, so I didn't book an blood test appointment for my son and we just walked in to the clinic. When we went there the receptionist explain to me that this is bot acceptable and I have to book an appointment. I explained to them that I have an list shows that I don't need an appointment and also I contacted the hospital to be sure that I would not need one. The whole staff was really rude and unprofessional and unfriendly and unhelpful this was my first time in this hospital and my experience was horrible.