Inaccurate estimate at in-network provider
I recently went to an in-network physical therapist, and I had asked for a cost estimate prior to the visit. They asked for my insurance details and got back to me with exact numbers for the cost of each visit before + after my deductible is met. After they submit the claim, my insurance is saying the "Patient Responsibility" is ~25% more than the estimate, and i now have outstanding bills from the physical therapist.
Why would the estimate with an in-network provider be inaccurate? I can understand it being wrong with an out-of-network provider (this happened to me at a dentist before), but I thought the whole point of an in-network provider was that there was a negotiated rate and a predictable cost? Is this normal, or am I missing something?