CHI St. Luke’s Health

I have contacted and spoke with my insurance, Cigna-HealthSpring, and specially with ChI St. Luke's Memorial Health Center (4 separate times) of Livingston and written two (2) letters regarding where I accidentially paid for my preventive care services performed at the CHI St. Luke's Memorial Health Center in Livingston. Cigna HealthSpring say I do not owe this bill as it is a preventive care service and per the benefits document, providers are not allowed to "balance bill". So I do not understand why I am not being refunded the $400 I paid by accident.