How common are insurance readjustments years after initial claim? And can they be disputed?

Hi all! This is my first time posting here and dealing with this issue so please excuse my ignorance and mild panic. For background, I am in NY and have Empire BCBS. But it is a high deductible plan so I am responsible for medical costs after any insurance discounts, as I never meet the deductible. It is serviced by a third party.

The situation: It seems my insurance company has reversed an adjustment for a service I received on 12/21/2022 and which I paid off in mid 2021. The service was for a breast MRI prescribed for me due to family history of breast cancer and dense breast tissue (I am under 40). At the time, the billed amount was for $2700 and the insurance discount was $1983 leaving my responsibility at $717. I paid that off directly to the prescriber by May 2021.

Two weeks ago, I received two more insurance claim summaries for this service. The claim docs themselves were difficult to understand. On one I saw that insurance wrote a check for $580 for this service, and wondered briefly if I was due a refund since they paid nothing in 2020. LOL… NO. After further investigation, I am seeing that their new plan discount amount is only $130 instead of $1983!!!!! So I am responsible for the remainder after my last years’ payments (and their new check amount), which is an additional $1270. I am very confused and stressed out, and just wondering how/why this happens. I need to call my insurance company ofc, which I am dreading bc they are so difficult! But that’s the only way to get direct answers. I am just curious if anyone has any experience with this sort of thing and can advise, both why it happens, what might have triggered it after more than a year and if there is anything I can do about it.

If more info is needed, happy to provide. Thanks so much for listening!