With bogus physician bills my SOP is to call the office and tell them that I will let the bill run to collection and dispute it in court. This strategy never failed, physicians are mortally afraid of having to admit that their billing practice is questionable.
With refunds from the insurance company I have found that a nice letter "please pay up 10 days from now or I will get a title in court" works wonders. I never had to no, not once.
More likely, doctors are very averse to lawsuits, and would sooner provide care to one patient at a loss than defend against a lawsuit, especially when it doesn't seem like a bluff because you seem like someone who could afford it (not typical btw).
With refunds from the insurance company I have found that a nice letter "please pay up 10 days from now or I will get a title in court" works wonders. I never had to no, not once.