Because you specifically instructed the doctor's office which lab to use, you may indeed be able to recover the cost of the testing, or at least the difference between what you would have paid had they used the lab you instructed and what you have in fact been billed for. It's possible that you could proceed on either or both of these theories: breach of contract (the doctor violated the "contract" between you and he for services by disregarding your instructions) or tort (by acting in a careless fashion in regards to your instructions, the doctor caused you a loss).You'll have to sue the doctor to recover  the money, if the office doesn't voluntarily pay you. Significant issues will be cost of proceeding (lawsuits are not free) and the fact that if you only provided oral instructions, those can be difficult to prove. If you can settle for any reasonable portion of the cost, you may wish to consider that a win.