Sonora Quest Laboratories – Billing never answers their phone

I've attempted now three times to get ahold of Sonora Quest billing dept. about a $729.00 bill. The first two times I was on hold for a minimum or 20 minutes, left a message, and never got a returned call. Today, I'm still on hold and it's been 38 minutes. I am not responsible for the bill and this is not the first time this has happened. Even their phlebotomists say they are aware that they never answer their phone. How is anyone supposed to resolve a billing issue if 'billing' can't ever be reached, and never responds to messages left?