Estimate of Cost runaround

I have a procedure scheduled for tomorrow. Communication about coverage and out of pocket costs was extremely last minute (just got the insurance approval letter yesterday after the provider office closed). I also got a call and voicemail from the billing department of my provider that I couldn't return yesterday. I tried today to return this call and no response even when trying multiple extensions, etc. I then tried to call my insurance company to get an amount the procedure will cost out of pocket. They told me they can't tell me even though I have a prior authorization. I also got an MRI about a month ago where my insurance company called me to tell me exactly how much I would owe beforehand. This has left me confused because the procedure tomorrow could potentially be very expensive. I realize that I could have been more proactive about trying to determine cost but this is where I'm at lol. Any tips to get an out of pocket amount from my insurance company?