Not quite sure which part you were billed for but if the "adjusted" amount was billed to you and ins. didn't pay for whatever reason (deductible not met yet?) You will owe the adjusted amount only, it's illegal for the provider to bill you for the pre adjusted amount or for the difference between the two.
Here’s an example:
The doctor bills $500.
On the bill it shows:
Total Charge: $500
Insurance Adjustment: ($400)
Amount Paid By Insurance: $00.
Amount Due From Patient: $100.
This happens all the time.