Insurance re-processed old claim and retroactively changed out-of-pocket maximum status

About three months ago, I had a hospital stay. It was billed through my insurance and my responsibility was a little over $2k. That’s fine, I had my FSA. So I took the money out of my FSA to pay for the bill. With the hospital stay, I reached my OOP maximum for the year (good thing for me, I’m chronically ill and go to the doctor at least once every other week for something, if not multiple times a week).

Fast-forward to this week, at one of my appointments, the receptionist asks me to pay a co-pay (strange because they knew prior that I don’t owe anything for the rest of the year). I call my insurance company and long story short, they retroactively reevaluated the claim from my hospital stay three months ago to technically benefit me (the amount I owed decreased by like $1200). However, it also removed my OOP maximum status. That would be okay if that was the extent of the change. However, I was reimbursed by my FSA, and I’ve had several doctor’s appointments over the past few months, of which the claims have already been processed and approved. With me owing $0 because of reaching my OOP maximum.

Basically, my question is what are my obligations here? FSA’s are taxed advantaged accounts, do I have to pay back my FSA? Was the reimbursement request now fraudulent because of the reprocessed claim? Do I now owe money for all of the doctors visits I’ve had over the last few months? How soon do I have to pay everything back? Will I be audited in someway?

Edit. I still have the EOB from the original claim if that helps in anyway. They never reissued an EOB for the updated claim.

Edit 2. I have Anthem BCBS