Question about Plastic surgery / anesthesiologist double dipping and getting payment from patient and insurance. Does this fall under no surprises billing act?

I got an elective liposuction procedure along with a belly button hernia repair, which were done at the same time. I paid in full for both procedures. The hernia repair was an extra $2900. The doctor’s office told me they would bill insurance for the hernia to see if I get back any money since it’s a medical procedure. He billed the insurance company $7500 and I ended up receiving a check from insurance for &800. Five months later, the anesthesiologist for the procedure full procedure charges my insurance company $7500 as well for the anesthesiology portion of the hernia repair. The insurance company then cuts me a check for $3200. Now the anesthesiologist office is hounding me every day for that check and I’m kind of unsure why I need to be paying them this check since I paid for the procedure in full. I did not sign any agreements with the doctor saying that I might have to pay extra anesthesiology fees. This was all billed through my plastic surgeon. The anesthesiologist called today and told me that they’re gonna send me to collections… But I don’t know for what since i don’t owe anything. This all seems kind of sketchy to me. Also, why is the anesthesiologist charging insurance the same amount the doctor charged? Do you have any advice on how to proceed?