Disputed medical bill effect on my credit report?

Hello. When I found out I was pregnant, my Dr's office ordered certain bloodwork from LabCorp. The nurse told me it would be covered by my insurance. I now get a bill for almost $200. My Dr. office tells me to contact the insurance company because my insurance company has always covered that test. My insurance company states that the test is not medically necessary & that they never cover that exam. I am now being thrown back & forth between the Dr. office & the insurance company. I understand that ultimately, bills are the responsibility of the patient however, had I been given correct information, I would have denied the test being done, especiallly it not being medically necessary. So, my question is: Since I refuse to pay this bill, can I dispute it with the collection agency once it gets there? I have PERFECT credit & therefore I am thinking that this $200 amount on my credit report cannot do too much damage, is this correct? How long will it stay on my credit report before it goes away? Thank you.