Medical billing error tally: $1900 and counting ...

I had heard that the medical system is rife with billing errors. But good god. So far, from The Big Hospital Adventure, we have:

-Received a bill for the ambulance that was an attempt at double billing -- we got one, and the insurance got one. When I called Aetna to ask if I should send the ambulance bill I had received their way, the agent said oh, hey, we already got it, but good thing you called, because it was processed wrong. Aetna initially processed it as 80% covered when our plan apparently calls for 100% coverage. Not that I would have known this, because none of the papers I've been able to get hold of address ambulance coverage. So, yay inadvertently catching the error?

-Received a bill sent to us with the note that the insurance company denied coverage. Why was coverage denied? Because the doctor's office billed the wrong insurance company.

-Almost left unchallenged $500 we weren't liable for after all. Apparently it's normal for doctors who visit you during a hospitalization to bill you (well, your insurance) directly, separately from the hospital's bills. One of the doctors who passed through was out of network. I was prepared to grump and suck it up and pay the higher out-of-network change (we've already hit our out-of-pocket limit for in-network expenses), until I mentioned it offhand to my new company's HR manager, during a chat about FSA options. She said that during hospitalizations, when you're not exactly in a position to doctor-shop, most insurance companies will cover out-of-network hospital-staff personnel as though they're in network. Hrm.

So I rang Aetna again today. Not only did that pan out, it turns out they had a precertification on file (two, actually) for this doctor's services. So, they had already approved in-network-rate coverage, but that information never made it to their claims department.

Aetna so far is not dazzling me with their competence at processing all this stuff, but at least it's been easy to clear up mistakes when I've called. I suppose I'm learning the frustrating way that once you get tangled up in the American medical system, be prepared to scrutinize and challenge every scrap of paper sent your way. And put your insurer's customer-service number on speed dial.