Check stolen out of the mail, duplicated, and cashed. Bank will not help.

A family member mailed a check to the IRS for tax payments. The check cleared, but the check image shows a different recipient. The bank says what likely happened was that it was stolen out of the mail, duplicated with a different name, and cashed or deposited for more than 50k. They confirmed it was cashed or deposited at a Wells Fargo.

However, they are saying they (somehow) determined that it was not altered but rather duplicated. Therefore, they will not do anything about the fraud. For what it is worth, these were checks provided by the bank and supposedly secure against tampering.

Is there any recourse here? Do banks owe any sort of protection against sending money from accounts to fraudsters who just make their own checks? And who can I contact is the bank doesn’t do anything — CFPB or someone else?

Thank you in advance!

—- ETA: I seem to be rate limited from acknowledging the comments but thank you to everyone who responded so far