I'm assuming that section 6 of your I-20 looks like this:
_{This school requires English proficiency.
The student has the required English proficiency.} 

This means you already have Eng language (TOEFL or IELTS or other) skills required  for the admission in your school. If it clearly says that you have the required Eng language proficeincy, why would they put you in ESL classes. I don't really understand.