ZT:
Unfortunately this is a scam some physician's offices run, claiming that they had no idea Lab X didn't take your insurance and better yet, they probably have a financial interest in it or they're splitting the reimbursement.
Almost all PPO contracts have a clause which states that a physician is supposed to use every effort to use another in-network physician, facility, lab, etc. This is forgiven more in a facility setting and especially in emergencies and in-patient stays but there's no real excuse for it in an office. Their claim is that they always can't keep track of which labs, etc. accept what insurance but you know what? That's what they have office staff for. To keep track of those things.
But that being said, the PPOs will rarely do anything to a provider that doesn't use 'every effort' to refer the patient to another in-network provider/facility/lab. Because if they did, they'd be kicking half of their physicians out of the network and then they wouldn't be making any money themselves.
If you're in an HMO then everything has to be in-network and if your doctor refers you out of it, that should be a violation of his contract and the HMO should discipline him. Which will probably do nothing to help your situation but at least demand they do something about it so it doesn't happen to anyone else, or you again for that matter. It really doesn't sound like that though or they would have told you something along those lines by now--there are PPO plans out there that also only cover in-network services and maybe that's what you have.
Filing an insurance commissioner complaint against your carrier more than likely isn't going to accomplish anything in this situation. They haven't done anything wrong but adhere to the terms of the contract. Like others have pointed out, the buck ultimately stops with you. Almost everyone gets burned like this by a physician's office once before they learn how the system works. Nowadays you just can't make the assumption that your physician's office has your best financial interests at heart. Ask pointed questions and if you don't get the answers you want to hear, street them and go to a new one. Good luck.