I would be livid also.

Just write down everyone you call date/time/who you spoke to etc..
Advise your Insurance company, If they have paid claim trust me they will demand repayment from the lab ASAP.
I agree with Eliza about contacting the Attorney General, just call them. then inform the lab you have already called no need to ***** foot around at this stage.

This will be all figured out in the end. I know this mess isn't doing you a bit of good.

I'm sorry