HMO MEDICAL INSURANCE WON'T COVER CHARGES?

I found out I was pregnant and had to attend a meeting out of state. While out of state, I was having bleeding and contacted the number in the back of the insurance card to get a hold of a physician so I can be seen. Physician ordered labs and so on. Now 3 months later, I get a bill from the physician and laboratory for 2k and insurance won't cover, they're saying that it wasn't authorized.