Then, you need to know your general deductible and copayment schedule. The bill should show original charges (fraudulent), "adjustments" to those charges to make them line up with what your "insurance" company has negotiated to pay, and then payment by the "insurance" company. The part remaining that you need to pay should line up with your deductible.
If you've got a large deductible (common) and this is one of your first bills, then the "insurance" company won't have anything to pay, but there will still be an adjustment. If you think that is off, you can contact your "insurance" company to check if it matches their negotiated rates. In my experience, their customer service departments haven't been totally gutted yet.
Calling the provider's billing department is generally pointless unless/until you know exactly what you're talking about. Once, a phone rep (at a small place even) called me to nag me about a bill. I told them that their charge was above the Medicare limit for a service, and that it needed to be corrected before I could pay. In response, they insisted harder that I "owed it" and I "had to pay". I told them they were wrong, ended the conversation, and just waited. Lo and behold 4-5 months later they finally billed the "insurance" and sent the correct bill. I think they were just hoping I'd fall for their fraud so they could pocket a few extra bucks.
I'm certainly not an expert on this subject in particular, just generally experienced at cutting through the avalanches of paper that psychopaths try to bury us with.
In practice how do you do this? I've never got a medical bill that made complete sense to me and when I did argue it went around in circles for so many months that it was not worth my time so I just paid it.