Help me dispute this surprise $600 bill I just got
Last year, when I was insured, I got an ultrasound at the hospital. Was billed a copay for $80, paid it, great. A year later, I get a surprise bill for $600. Apparently they started billing my insurance two months after my visit, with no response from my insurance. In the bill I see 11 attempts, of three different medical codes, all ignored. Starting at $134, then $300, now $600. Finally, they're billing me.
My question is, how do I dispute this? I was insured. I was not made aware of my insurer's lack of response even one time in the whole year since I had treatment. Now due to their lack of response, it's my responsibility to pay?
Who do I contact first, what do I even say?