If the doctor in fact directed the hospital to perform an MRI on the wrong area of your body, you could arguably sue him for negligence and ask for your co-pay amount as damages. The problem for you would be that suing a physician for medical malpractice is both very technical and an expensive proposition. The cost of your suit would likely be far more than you could reasonably expect to recover from the doctor, even if you win. You can also expect that the doctor may claim that an MRI of the hips was necessary because you either reported some pain in that area or the doctor suspected that some of your low back pain was possibly referred pain from the hip area (thus making an MRI of the hips appropriate).
My best suggestion is that you schedule another appointment with the doctor to follow-up on your problem and at that appointment explain what happened and ask him to "do the right thing" by paying the copay for the incorrect procedure. If he declines, you can report his conduct to the Florida Department of Professional Regulation but there is little else I think you can reasonably and economically do.
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