Bill from eye exam from last year

Hi,

I just received a bill for an eye exam from over a year ago. How long do insurance companies have to process a claim and send me the bill? At what point am I freed from that obligation due to their negligence?

Also, my health insurance has changed since then; they listed me as uninsured for that appointment, when it should be fully covered by my insurance at the time. How'd they mess all of this up?

Please help.
Thanks!

I didn't find the right solution from the Internet.

References http://www.medhelp.org/posts/Health-Insurance/Bill-from-eye-exam-from-last-year/show/2043294

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