Dupage Eye Surgery Center

Very confusing billing. Went to the Wheaton Eye Clinic for eye vision complication and subsequent required surgery. Had surgery performed at the Dupage Eye Surgery Center. While I paid all bills in a timely manner to the Wheaton Eye Clinic, I was not aware that I would also be billed separately from the Dupage Eye Surgery Center as I had assumed the Wheaton Eye Clinic and Dupage Eye Surgery Center were the same entity. I have now had my bills from the Dupage Eye Surgery Center turned over to a collection agency. When I contacted the Dupage Eye Surgery Center to correct this payment problem, and make payment, I was informed that they are separate from the Wheaton Eye Clinic. Very confusing as even their website leads one to believe they are the same entity. I never received a copy of any documents from the Dupage Eye Surgery Center indicating that I had signed an agreement clearly stating that Dupage Eye Surgery Center would bill me separately and any unpaid bills would be turned over to collection agency at a stipulated interest rate.