Challenging a hospital bill for medically unnecessary procedure

My wife and I received a large medical bill for an MRI performed on our 10 m.o. son last month. The bill is from a major Houston hospital. The pediatric neurologist who examined our son at the hospital's Austin clinic told us that we likely didn't need an MRI at this point, but that it wouldn't cost us anything besides a trip to the hospital in Houston.

The MRI results came back completely normal – thank God! But had we known the size of the bill, we wouldn't have done it, because the neurologist made it clear that it wasn't necessary yet.

Has anyone encountered a situation like this – either on the patient side or provider side (or insurance side?)? Any pointers are appreciated.

​