Will they cover the fee for the accountant to fix their own mistake?
https://www.irs.gov/faqs/irs-procedures/refund-inquiries
If the check was not cashed, you can get it canceled and a new one mailed.
And yes, I've dealt with the IRS a few times some of which they owed me money. It is a bureaucracy, but the process will work even if it takes a bit of time.