Here is a link to how BCBS of Illinois (my BCBS payer) handles refund requests:
https://www.bcbsil.com/provider/claims/refund_management.htmlYou should go to the website for your BCBS payer, and see what information is there for how they handle these requests. I have never heard of any BCBS in any state just taking back the money through offset, without notifying the provider first in some fashion. Obviously having the provider rep help you is the first step, but seeing as how yours is ignoring calls/emails, you need to look at other methods of getting to the bottom of this also.
You should also see if Availity has an Electronic Refund Management tool like we have for BCBS of Illinois, because then if you register for it, you can see all the requests, and dispute them if necessary. It will also send you emails when a new request is added.
Also, it sounds to me like BCBS has identified something in the way the claims were billed/coded that has caused them to go back through everything submitted in the past and make a mass adjustment for over-payment to your provider. I saw this happen with a doctor who was billing a certain type of very expensive injection for awhile, and eventually BCBS figured out that he was an outlier in how he was billing it, and that he incorrectly coded his claims/lacked medical necessity for the injections. They sent him a letter saying he owed BCBS over $200,000, and he won't see payment from them for a long time. I am not saying your provider has done anything illegal, just that BCBS has found some sort of very large irregularity if they want that much money back.