Therapist’s office claims insurance didn’t cover 13 appointments and now we owe 2600 dollars?

My husband started seeing a new therapist in March, he was referred by his psychiatrist because they accepted his insurance. The counseling office said his payment was 20 dollars… five months and 13 appointments later they are saying that his insurance didn’t actually cover and he owes the office 2600 dollars.

He is a full time student and we do not have the money to cover this. It feels like a fraud.

Advice on how to handle this situation? Shouldn’t they have told us this after the first or second appointment?