Got charged 5400$ for basic lab tests for preventative exam

recently took some lab tests as part of a preventive exam, and when I checked my insurance portal, I noticed three bills. One bill is for $300, and I don’t have to pay anything for it. The second bill is for $125, which is also covered. But there’s a third bill for $5,400, and this claim is still under processing.

These are the tests I took: CBC CMP , serum or plasma Lipid panel, serum TSH + free T4, serum HbA1c (Hemoglobin A1c), blood

All I did was have two appointments with an internal medicine provider—one for a new patient visit to find out what tests I needed to take, and another follow-up visit to discuss the results and get a signature on a letter for my employer as part of my annual checkup.

Is this amount common for such basic lab tests? This is my first visit to a hospital in the U.S., and I’m confused about why I’m being charged so much.

who should I reach out to in order to inquire about this huge bill—the insurance company or the hospital? Thanks in advance.