I Was Admitted To ER Last Weekend With Severe Fever,

I was admitted to ER last weekend with severe fever, chills and pain in rectum. I was diagnosed of having rectal abscess and was taken as inpatient and rectal surgery was performed. I stayed in the hospital for 2 nights. Now my health insurance has rejected the 35000 hospital bill stating that this surgery doesn't qualify for inpatient hospital stay. Not sure what I should be doing now. This is giving me the real pain in A**. Should hospital bill them as observation rather than inpatient? Please help me with suggestions.