Complaint Review: mollen immunization clinics

So my family was shopping at Walmart #2131 and I saw they were giving flu vaccines. So I went to talk them about the nurses qualifications and insurance coverage. She took my insurance card enter it into her lap top and said it would be covered 100 percent so three of use recieved the flu shot. Then I recieved a bill in the mail for a total of 75$. When looking that bill the insurance was BCBS of Rhode Island and we have BCBS of South Dakota. When I called Mollen they said it was entered in error. So I said how can that happen when she had my insurance card right in front of her. They had no answer for this. I believe this nurse knew they didn't take my insurance and put in Rhode Island so I would think it was covered. I also believe she was trained to do this to recieve incentives for the amount of immunizations they give......no I have no proof of incentives but what else would make sence? There is a huge difference between South Dakota and Rhode Island. I have learned m y lesson and next time will go with our doctors office but I shouldn't have been scammed just so the company would get an extra 75$.